which he re-named Lake Leopold. Mr. Thomson did not succeed in reaching the actual shores of the lake. "The point where we halted was upwards of 7000 feet above the sea, and from the fact that the River Mkafu, which flows into the lake, is only about 3000 feet, at a distance of sixty miles north, I infer that Lake Hikwa is not far from being on a level with Tanganyika. So steeply do the mountains descend, that from the place where we halted we could almost throw stones into the lake; only we lost sight of them before they reached the ground. The general altitude of the surrounding ranges must be quite 8000 to 9000 feet, and they extend in a quite unbroken line all round. At the north end I calculate the breadth of the lake at about twelve miles. Further south the breadth varies from fifteen to twenty miles. Longitudinally it lies north-north-east and south-southwest. Its length, from native report and from my proximity to it in passing between Nyassa and Tanganyika, I conclude to be certainly not less than sixty miles, probably seventy. Between the mountains and the shores there lies a narrow dark green strip of smooth land, apparently representing a once higher level. On this there are many villages, and the ground is highly cultivated. At the north end, as I have already stated, this strip broadens out into a marshy expanse, formed doubtless by the detritus of the River Mkafu." Marine Alga of New England and the Adjacent Coast. Although the waters are almost certainly fresh, yet the England are thus furnished with a handy and compact lake seems to have no outlet. Without accident or obstacle to speak of, the Expedition, proceeding by Unyamyembe, reached Zanzibar, not much more than a year after it set out from Behobeho. Mr. Thomson, with good reason, congratulates himself that he never needed to fire a shot either in offence or defence, and that, besides the loss of Mr. Johnston, he left only one man behind him. The Expedition is in many ways one of the most successful that ever entered Africa. Not only was it conducted with unusual efficiency, not only were the chiefs and people, with few exceptions, friendly throughout, but for the first time we have obtained trustworthy observations on the geology of the great lake region of Central Africa. The main conclusions reached by Mr. Thomson have already been described by himself in these pages. But he did not confine himself to geology. He gives us a fair idea of the general character of the country traversed, its mineral, vegetable, and animal productions, the characteristics and habits of the people, the nature of the work being done by missionaries, and the capacities of the country for industrial development. On the last point his views are far from being sanguine. He maintains that the resources of Central Africa have been greatly exaggerated, especially as to its minerals. We are inclined to think that on this point he has taken much too gloomy a view, and that, whatever may be the case with the region actually visited by him, there certainly appears to exist, in the districts traversed by Cameron, Livingstone, and more recently by Major Serpa Pinto, stores of iron and copper that may at a future time be turned to great industrial account. Young as Mr. Thomson is, we commend his remarks on missionary work to those whom it most intimately concerns; and we trust that his severe, but evidently just, criticisms on the conduct of the various Belgian expeditions in Africa will receive the attention they deserve from the management Since the appearance (1852-57) of Harvey's classic work on the North American Algæ, but few species have been added to the Flora. This is not perhaps so surprising as regards the Florideæ or Fucoids, to which Harvey paid so much attention; but as regards the uni cellular or simple filamentous forms it is a cause of surprise, for Harvey never paid minute attention to these; and it may in part be accounted for that collections do not seem to have been made along the coast in spring. graphical distribution of the species met with. Cape Cod Prof. Farlow gives a most interesting sketch of the geois, as was known to Harvey, the dividing line between a marked northern and southern flora, and subsequent observation shows that on the one hand the flora north of the Cape is more decidedly arctic than he supposed, and that on the other hand that south of the Cape of the commoner species are also natives of Great is more decidedly that of warm seas. A good share Britain, another large share are Scandinavian; but while this is the case the marine flora is also marked by the complete absence of many common British species. No members of the order Dictyotaceæ are to be found; no species of Cutleria or Tilopteris are to be met with. The species of Nitophyllum may be said to be wanting. That commonest of our red sea-weeds, Plocamium coccineum, is known as native by only one doubtful case. Fucus canaliculatus, Himanthalia lorea are quite wanting. The nearly ubiquitous Codium tomentosum has not yet been found. Fucus serratus is very rare, having only one locality recorded for it in the United States and one in Nova Scotia. Gelidium corneum, abundant in almost all parts of the world, is only occasionally found in New England, and then only in the starved form known as G. crinale. Prefixed to the orders and genera will be found carefullywritten diagnoses, and an artificial key to the genera is also added. The notes in smaller type which are given under the species often contain most valuable critical information, which will command the attention of all phycologists. To the critical students of our native species of alge this little manual of the New England species will prove a most welcome volume. They will find in the chapter on the structure and classification facts that were not known in Harvey's day, and which, here collected for them within a brief space, they would otherwise have to search for in the writings of Thuret, Bornet, Janczweski, Rostefinski, Pringsheim, or Reinke. The Berries and Heaths of Rannoch. (London: G. Bell and Sons, 1881.) THE berry-bearing plants here described and delineated are eight, viz. Vaccinium oxycoccos, V. Myrtillus, V. uliginosum, V. vitis Idea, Arctostaphylos uva-ursi, A. alpina, Empetrum nigrum, and Rubus chamamorus, all of which do not, strictly speaking, come within the geographical limitation of the title-page. The heaths are three only in number, viz. the common Erica cinerea and Tetralix, and Calluna vulgaris, to which are added two other nearly allied species not actually found within the district, Andromeda polifolia and Loiseleuria (Azalea) procumbeus. In the letterpress it is not to be expected that anything new could be added to what is already known about these plants; but in an appendix is given a list of the Gaelic names of the various species supplied by the editor of the Scottish Naturalist. The coloured plates are exceedingly good and characteristic; but surely it should have been stated that they are taken from Sowerby's "English Botany." The volume is a pretty one to lie on the drawing-room table. A. W. B. Lehrbuch der Mineralogie. Von Dr. G. Tschermak. I. Lieferung. (Wien: Alfred Hölder, 1881.). IT is with great pleasure that we have received this instalment of Prof. Tschermak's work, and also learnt from the publisher's introductory note that the rest of the book may be expected during the course of a year. The work is sketched somewhat on the lines of Naumann's wellknown "Elemente der Mineralogie," but follows Miller's Mineralogy in the wider scope given to mineral physics. The present number is introductory, and treats of descriptive crystallography, crystal-structure, general mineral physics, and includes a considerable portion of mineral optics. In the crystallography the Millerian notation and the stereographic projection are employed, and the systems are developed from the principle of symmetry in a clear and simple manner. Prof. Tschermak has adopted the four-plane axial system in the rhombohedral system, which is sometimes designated the Bravais-Miller system. Possibly this may appear to non-mathematical students simpler, and may to a certain extent be more easily mastered, but we feel sure that in its practical application to crystallographic problems it does not possess either the elegance or conciseness of the three-plane axial system selected by Prof. Miller. We feel also that it is most unfair to Prof. Miller's memory to attach his name, even in a double-barrelled way, to a system which he steadily refused to adopt. The theories and facts of twin and mimetic crystals are carefully expounded. These constitute a branch of mineralogy which has become of the utmost importance since the application of the microscope in the investigation of the optic properties of minerals. Other sections, which are especially good, are those on mineral inclusions, on the hardness and etching of crystal faces. These contain a large amount of information which is rarely to be found except by a laborious search through scientific periodicals. The book is divided into sections, each dealing with its separate subject, and at the end of each section is a list of the more important literature of the subject. The work so far is excellent, and if, as we have every reason to expect, it be carried through in an equally satisfactory manner, we shall possess a text-book in keeping with the reputation of its author and worthy of the school to which he belongs. W. J. LEWIS LETTERS TO THE EDITOR [The Editor does not hold himself responsible for opinions expressed by his correspondents. Neither can he undertake to return, or to correspond with the writers of, rejected manuscripts. No notice is taken of anonymous communications. [The Editor urgently requests correspondents to keep their letters as short as possible. The pressure on his space is so great that it is impossible otherwise to ensure the appearance even of communications containing interesting and novel facts.] Panizzi and the Royal Society THE "Life of Panizzi" by his friend and colleague, Mr. Louis Fagan,1 is marked by a tone of indiscriminate adulation which disfigures many specimens of modern biography. The hero is perfect, and they who think otherwise are dismissed with words of contempt, or are admonished to go and meditate on their wicked ways and then return in repentant mood to the community of hero-worshippers. In the Royal Society's treatment of Panizzi, Mr. Fagan endeavours to justify another example of the wolf and the lamb, although it must be owned that in the pamphlets from which getic to lead to the conclusion that he thought himself a match the biographer quotes, the lamb's bleatings are sufficiently ener for the wicked wolf. Mr. Fagan thinks it important "that Panizzi's stormy connection with the Royal Society should be fairly and impartially " stated; although how this can be done without hearing both sides he forgets to say; and yet he professes to give "the proper elucidation of the facts,' ""the whole circumstances of the case thoroughly weighed and dwelt upon"; how successfully he opposed the force with which it was attempted to crush the evidence of his superior talent" (vol. i. p. 119), and although "thwarted and impeded at every step, Panizzi at last succeeded in once again proving that right can contend successfully with might" (vol. i. p. 130). The reader will gain a very lop-sided idea of this quarrel if he trust to Mr. Fagan's account alone; and as in the reviews of this book no one has attempted to ascertain the truth of the matter (which indeed could not be done without access to the Royal Society's papers), I venture, as a member of the present Library Committee, to state the case from the other side, being naturally anxious to sustain the reputation, so unjustly assailed, Baily, Beaufort, Children, Greenough, Lubbock, Murchison, Peacock, Roget, and others.3 of a former committee which contained the honoured names of To make a long story short, it is sufficient to state that about the year 1832 the Royal Society wished to bring out a complete catalogue of the books, &c., in its library. As a preliminary step, a list of the mathematical books was compiled and set up in type as a specimen of the kind of work required. In the words of a Council minute, the sheets were "not designed for publication," they being "in a very rough and unfinished state." In October, 1832, Dr. Roget meeting Mr. Panizzi at dinner, look over and revise the sheets in question, together with others informed him of the Society's intention, and requested him to that might afterwards be forthcoming. This was agreed to, and the first sheets were forwarded to Panizzi, who found so many errors in them that, as he informed Dr. Roget, "although I would never attempt to correct what had been already done, I was ready to undertake a new compilation." Accordingly on October 16, 1832, the Library Committee resolved to recommend to the Council that Mr. Panizzi be engaged to make a new catalogue according to the mode to be agreed upon by the Committee, he to be paid 30/. for every thousand titles, the whole remuneration, however, not to exceed 500%. "The Life of Sir Anthony Panizzi, K.C.B." By Louis Fagan. Two vols., 8vo, 1880. 2 "A Letter to H. R.H. the President of the Royal Society, on the New Catalogue of the Library of that Institution now in the Press. Pp. 56 and 3. Signed A. Panizzi, and dated January 28, 1837. The last three pages contain a postscript letter to the President, dated November 4, 1837, and a note in which it is stated that the pamphlet was not put into circulation until the latter date, in order that H.R. H. might have an opportunity of replying to it. The President, not having availed himself of this opportunity, the second pamphlet was put forth. It is entitled "Observations on the Address by the President, and on the Statement by the Council to the Fellows of the Royal Society respecting Mr. Panizzi, read at the general meeting, November 30, Dated December 22, 1837. 1837 Pp. 24. Strictly speaking there were three committees, namely, one for the catalogue, a second for the library, and a third for deciding in doubtful cases under what division a book should be placed in the new catalogue. Panizzi agreed to these terms, and offered "to wait on the Committee, as scon as convenient to them, to settle the manner in which they wish the work to be executed." Now the whole gist of this quarrel consists in this, that the Library Committee naturally wished to control Mr. Panizzi in in his mode of executing the work, while he refused to be controlled or interfered with in any manner. He even regarded as personal enemies all those who attempted so to interfere. He fancied that every one who differed from him was actuated by a sense of personal dislike. When he refused Dr. Roget's request to revise the sheets of the Catalogue, he says (p. 6): "I had no idea when I so candidly expressed my opinion that I was making a powerful and unrelenting enemy in one of the most influential officers of the Royal Society." At p. 51 he says: "so gratuitous an insult would never have been allowed had not Mr. Baily filled the chair at that meeting." And again (p. 5), "My statements will be received with derision by those who know that they may be unjust with impunity." At p. 18 he charges the Committee with "indelicate conduct," at p. 22 with "absurdity," at p. 25 such things were done "purposely to annoy me; and again, "No suggestion of mine would ever be attended to by the Council. At p. 26 his work was regarded with "a malignant eye;" at p. 28 "The annoyance was incessant," "injurious and unjust;" at p. 33, "treating me as if I were their servant," "unwarrantable liberty;" p. 38, "unjustly interfered with;" p. 41, "insulted with an order of submitting my work to revision. . . . I shall never consent for any one, be he who he may, to make any alterations in it.' And when, on June 24, 1836, he was requested to attend the Library Committee on the following Monday at 4 p.m., he declined on the ground that "when I attended before I was not so well satisfied with my position as to wish to be in it again." At p. 54, when clamouring for payment of an unascertained balance which he claimed, he charges the Council with not meaning "to pay it unless they be compelled to it. . . . Possibly there is some legal means of obtaining redress; but in a country like this justice is not a luxury for a poor man to indulge in; and the Council, having at their disposal the funds of the Royal Society, can amuse them. selves without personal trouble or loss with a law-suit which I have not the means of sustaining." Will it be believed, in the face of such language as this that Panizzi had already been paid the sum of 4507., and his whole remuneration was not to exceed 500%. In his second pamphlet (p. 18), after charging the Council with not meaning to act fairly, he hurls at it his "unmixed disgust and contempt." But I cannot help thinking that these vigorous epithets would have been more appropriate had they travelled the other way. When requested to return the printer's revises, and he refused on the ground that they were his own property, together with the key of a drawer in one of the Royal Society's rooms, and he also refused, what wonder that, after so long a contest with this cantankerous man, the Council should have resolved on July 14, 1837, "that Mr. Panizzi be no longer employed in the formation of the Catalogue." The reader may well exclaim by this time, What is all this hubbub about? Simply this: Mr. Panizzi insisted on adding to some of the items of the Catalogue original comments of his own, to which the Library Committee justly objected as committing the Society to opinions of doubtful value. Panizzi attached the greatest importance to these notes and comments. "The Committee, far from objecting to them, ought to have been thankful that I had taken the trouble of introducing them " (p. 31); and he proceeds to quote specimens illustrative of this part of his work. For example, he says: "To the Mémoires' of Charnières on the observations of the longitude, I added this note: All the author's additions and corrections carefully put in by J. B.' This note is on the title-page of this copy, and the volume is interspersed with alterations in manuscript. I suppose J. B. to mean James Bradley." Later on in the same page he adds: "The author's additions, if put in by Bradley, are, of course, of much more value than if written by any other J. B." Now the book in question is only a single Mémoire of De Charnières, not a collection of "Mémoires," as described by Panizzi. Moreover, there are five reasons why the additions and corrections could not have been written in by Dr. Bradley. 1. He died five years before the memoir by Dr. Charnières was published. This may well excuse the other four reasons, but they are curious as illustrating the carelessness of a man who was convinced of his own infallibility. 2. The writing of the anonymous J. B. is small and neat: that of Bradley large and awkward. The Royal Society had in its possession manuscripts of Bradley and his signature, which could be seen by merely a king the assistant-secretary for them, and yet Panizzi did not submit the writing of J. B. to this simple test, 3. Bradley was not in the habit of writing in his books. 4. The so-called "additions and corrections" are simply the corrigenda collected into eight pages at the end of the book, and transferred in MSS. to the text, a fidgety piece of work, not likely to be undertaken by so busy a man as Bradley. 5. At the end of the book J. B. drops his incognito and appears as 7. Bevis, a fact overlooked by Panizzi. Other similar examples might be given, and indeed were submitted to the Fellows of the Royal Society at the time, order to justify the resolution of the Library Committee "that all comments or notes expressing matters of opinion on the articles in the catalogue be omitted"; but the statement of them would occupy too much space, dealing as they do with details which unless given in full would not be understood. Mr. Panizzi was undoubtedly a vigorous clever man; but in the matter of books, he, unfortunately for his own reputation, aspired to universal knowledge which belongs to no one. The gold of a universalist is apt to shrink down into dress when tested in the crucible of a specialist. Having occasion to consult a book by Gay-Lussac, and not finding it in the Catalogue of the British Museum Library, the attendant requested me to write the name and title on a slip and show it to Mr. Panizzi. No sooner had he glanced at the slip than he exclaimed "Ah! you have made a mistake: it is Guy-Lussac! This readiness on all occasions to say something apparently to the purpose, may impress subordinates with a sense of power on the part of their chief, but to tell a chemist that Gay-Lussac is Guy-Lussac would be much the same as telling him that potash and soda are identical compounds. C. TOMLINSON Highgate, N., August 2 The Oldest Fossil Insects IN a paper on "The Devonian Insects of New Brunswick (Bull. Mus. Compar. Zoology, 1881, vol. viii. No. 14) I have drawn attention to the fact that a fern on the same slab with Platephemera was determined in 1868 by Prof. Geinitz as Peco pteris plumosa, and therefore the slab considered by him as belonging to the Carboniferous. I believed that here an impor tant gap was still to be filled, namely, the reliable determination of the fern, which is not mentioned in Mr. S. H. Scudder's monograph, nor in Principal Dawson's note on the geological relation of those insects, which closes Mr. Scudder's paper. A paper by Mr. Dawson (Canad. Naturalist, 1881, vol. x. No. 2) is intended to fill this gap. The fern is after the study of the original specimen determined as Pecopteris serrulata, and said to be a common species in those beds. If I am not entirely mistaken it will be difficult to agree with Mr. Dawson's opinion (.c. p. 2) "that doubts and suspicions thus cast on work carefully and exhaustively done should not seriously affect the minds of naturalists," as it happens that in his work of 1880 this common species is not quoted at all among the plants found in those beds, except in a note (p. 41) stating that in the beds 6 to 8 three or four other species occur, among them probably P. serrulata. Mr. Dawson quotes for the species the figures 207 to 209 in his Report of 1870, but I confess to be unable to recognise the Platephemera fern in those figures. Prof. O. Heer has kindly drawn my attention to his "Flora Fossilis Arctica of Bear Island, Spitzbergen, 1871." He has given (pp. 14, 15) a detailed review of the fossil plants from St. John's, New Brunswick, and, as he still believes, has proven that those layers do not belong to the Devonian but to the Ursa stage of the Lower Carboniferous. This important and elabo rate statement is disposed of by Mr. Dawson, as far as I know, only in his report, 1873, p. 8, in the following words :-" The so-called Ursa stage of Heer includes this (Lower Carboniferous), but he has united it with Devonian beds, so that the name cannot be used except for the local development of these beds at Bear Island." It is true that Mr. Dawson, in the supplement to the third edition of the "Acadian Geology," 1878, p. 72, has tried to duction of the Paleozoic flora in American formations. But explain the different opinion of Prof. Heer by the earlier introthis fact, known by every one, and of course by Prof. Heer, is not considered by him to be a sufficient objection to the statements given in the "Flora of Bear Island." The paper of Prof. Heer states carefully and exhaustively the The True Coefficient of Mortality THE very interesting and suggestive lecture of Alexander Buchan on "The Weather and Health of London" (NATURE, vol. xxiv. p. 143 et seq.) reminds me of the propriety of calling the attention of writers on "vital statistics" to a point in relation to the true method of discussing the mortuary data. The specific point to which attention is drawn is the necessity of estimating the relative tendency to special diseases by comparing the number of deaths from the given cause with the number of persons living at the ages embraced in the record; instead of making the comparison (as is usually done) with the total deaths from all causes, or with the total number living at all ages. In like manner, in discussing the influence of age on the mortality from any given disease, it is very common to prepare tables of the number of deaths at each age, and in some instances these numbers have been assumed to represent the relative tendency to the disease at different ages. It is scarcely necessary to say that this is a very serious error, for it must be borne in mind that the number of persons living at different ages is very unequal. Indeed it is self-evident that the true coefficient of mortality for any given disease at any given age is expressed by the ratio of the number of deaths from the specified disease at the given age to the number of persons living at the same age: or, as it may be otherwise indicated, the number of deaths from the given disease at the given age per 1000 persons living at the same age. In illustrating this point I shall select cancer, because, in relation to the influence of age, it furnishes an extreme case, and thus affords a glaring instance of the fallacy of taking any basis of comparison other than the number of persons living at each age. The mortuary records of the Department of Seine in France, during the eleven years, from 1830 to 1840 inclusive, furnish a total of 9118 deaths from cancer, 2163 males and 6955 females. The following table relating to the mean annual mortality from this disease among females will illustrate this point : The foregoing table demonstrates the inaccuracy of the popular impression that the tendency to cancer attains its maximum between the ages of 35 and 50 years. The numbers in columns (3) and (4) might seem to support such an opinion; but, as we have seen, those in column (5) are evidently the true indices of the tendency to this disease at different ages; and it will be observed that the mortality goes on steadily augmenting with each succeeding decade of age up to 90 years. The fact likely to be most strongly impressed on the reader by the numbers in column (5) is the remarkable regularity of increase of the co efficient of mortality for cancer with advancing life among females after the age of 25 or 30 years. Between the ages of 25 and 75 the mortality increases nearly in arithmetical progression as the age advances in arithmetical progression, the average increment being about 1.30 per 1000 living at each age for each decade. Assuming this to be the law of mortality from cancer among females, it admits of very simple mathematical expression. Thus, let A A': C the age at which liability to cancer begins. = constant coefficient, variable according to country, state of civilisation, &c. Then we have-Annual mortality per 1000 living at age A' = C (A' - A). = In our table representing the mortality from cancer in the department of the Seine from 1830 to 1840 inclusive, the value of A may be taken = 25, and C 0'13; hence we have-Annual mortality per 1000 living at age A' = 0·13 (A-25). Thus by the formula the mortality at 55 3'90, and column (5) gives 4'00 between 50 and 60; at 75, formula = 6'50; table = 6'49 between 70 and 8o. The mortality from cancer seems to be vastly smaller in Eng. land than it is in France, so that a less value must be given to the constant C. The foregoing formula represents the law of increasing mortality with advancing life in the simplest form, as a function of the age. This extreme simplicity is probably unique in the case of cancer, and seems to indicate that age is so far the controlling element in the development of this disease as to overpower all other causes. In the case of other diseases we cannot expect to escape the necessity of employing those exponential functions in investigating their laws of mortality, which are essential when a multiplicity of causes are operation. in Many years ago the attention of the medical profession in this country was called to the fact that the available mortuary data were not discussed in a manner which revealed the true value of the facts contained in the numbers. But there is reason to believe that Prof. Francis A. Walker, the intelligent superin. tendent of the census of the United States for 1880, will not overlook this point when he comes to the discussion of the mortuary statistics which have been collected. Berkeley, California, July 7 JOHN LE CONTE [Mr. Le Conte does not appear to have apprehended the point discussed in the lecture on "The Weather and Health of London"-that point in no part of the inquiry being the tendency to the disease at different ages, but the manner of the distribution of deaths in the case of each disease through the weeks of the year, with the view of arriving at some knowledge of the influence of season in determining that distribution. Only in one case, viz., in discussing the rates of the mortality from diarrhoea in several large towns, was a reference to population required, and in that case the curves were drawn, showing the weekly rate of mortality per 1000 of the population of the respective towns.-ALEXANDER BUCHAN.] Bisected Humble Bees I TOO have frequently observed humble bees lying dead or stu pefied under lime-trees, sun-flowers, and some other plants, and once I saw a Staphylinus, commonly known as Black Cock-tail, or Devil's Coach-horse, nip a humble bee in two, and on passing that way later I found that it had cleared out the honey-bag and left the two halves of the bee on the path, as described by your correspondent. I have known boys catch humble bees and eat the honey in them; and probably many other animals have learned how to get at the sweet drop. Trinity College, Cambridge THOS. MCK. HUGHES I NOTICE the same phenomenon here, under the sycamore trees, when they are in blossom, which your correspondent Mr. Masheder observed recently under his lime trees, namely, the heads and thoracic segments of severed humble bees lying on the ground, with legs and wings attached, still retaining their vitality in some cases, but without any trace of the abdominal segments, for the sake of whose contents, no doubt, the bees were destroyed. We have no fly-catchers here. I suspect the tomtits, which are abundant in the vicinity of this wholesale apicide, but I have no direct evidence of their guilt. R. V. D. Beragh, Co. Tyrone, August 15 Migration of the Wagtail Apropos of recent letters on this subject in NATURE, permit me to note that on my voyage out to the East Indies in the month of October, 1878, on board the Dutch mail steamer Celebes, two wagtails alighted on the ship when not very far north of the equator (the ship's course being then from Aden to Padang in Sumatra). On observing them I pointed them out to a Dutch friend, who at once recognised them as Kwikstails. They were rather lively, and did not appear to us to be fatigued; after staying with us for some days they took their departure, but in what direction I had not the satisfaction of observing. Without affirming positively, I believe the species was the Motacilla alba. HENRY FORBES Sumatra, June nately reinforce and interfere with one another, and produce the throbbing sound of beats, the number of beats (or maxima of sound) per second being the same If one tone makes m vibrations per second and the other as the difference in the number of vibrations per second. n (a slightly smaller number, being a slightly flatter tone there will be m-n beats per second heard. If this number be not more than 3 or 4 per second the beats can easily be counted. When they get as rapid as 12 or 14 per second they come too fast to be counted, and are very harsh and grating. They are most disagreeable at about 33 per second; and if yet more rapid, are heard as a harsh, disagreeable, rattling sound quite different from a true note. Imperfect octaves and imperfect twelfths likewise cause beats; in fact there are beats heard for any imperfectly tuned consonance in which the frequency of the higher note is 1, 2, 3, 4, 5, . . . or any integer number of times that of the lower. But along with the disagreeable and throbbing phenomenon of beats there arises another phenomenon when two notes not in unison with one another are simultaneously sounded. This is a low booming tone, to which musicians give the name of the "grave harmonic." If two stopped organ-pipes are brought to unison, and then one of them is sharpened by gradually pushing in its stopper, the beats are heard first slow, then fast, then unendurably rapid. But when they reach about twenty or thirty per ITALIAN DEEP-SEA EXPLORATION IN THE second the low booming note begins, and rises gradually MEDITERRANEAN AFTER some delay, beyond our control, the warsteamer of the Italian Royal Navy Washington, Capt. G. B. Magnanghi, R.N., left Maddalena on the 2nd inst. on her thallassographic mission. Under the able direction of Capt. Magnaghi, two days were devoted to preliminary dredgings and trawlings in depths from 200 to 1000 metres, principally for testing our apparatus, which works admirably. On the 4th inst. (yesterday afternoon) we did our first deep-sea dredging in 3000 metres; the dredge came up empty, but I had the pleasure of securing, attached to the hempen tangles, a magnificent specimen of that strange blind Crustacean discovered by the Challenger in the North Atlantic, and named Willemasia leptodactyla; it is no doubt one of the inost characteristic forms of the deep-sea fauna, and its discovery in the Mediterranean is of very great importance and interest, as all students of thalassography will be fully aware, after what Dr. Carpenter has written on the biological conditions of the deeper parts of that sea. Our specimen of Willemæsia is slightly smaller than the one dredged by the Challenger, and figured in Sir Wyville Thomson's 66 Atlantic," vol. i. p. 189; but otherwise it differs only in one or two minor details, which may be sexual differences; it was dredged off the west coast of Sardinia. On account of a slight mishap with our engine we have anchored at Asinara for a couple of days, but shall at once resume our work. HENRY H. GIGLIOLI Asinara, Sardinia, August 5 KÖNIG'S WAVE-SIREN E VERY musician is painfully familiar with the fact that two notes nearly, but not quite exactly, in unison with one another, produce, when sounded together, a throbbing sound commonly described as the phenomenon of "beats." In the elementary theory of acoustics the cause of beats is shown to be the mutual interference of the two vibrations, one sound interfering with the other and silencing it, when one set of waves is half a vibration behind the other. Just as at certain points on the earth's surface there are no tides when a high tide and a low tide coming from different seas meet, so there is no sound when two sets of sound-waves meet in opposite phases. If the two notes differ just a little in pitch they will alter in pitch as the beats become too rapid to be discriminated. When the higher note has reached a point about half-way between unison and the octave note, the beats are practically imperceptible, and from this point the phenomena recur again, but in inverted order, the grave harmonic falls in pitch down to a low booming tone, while the beats begin again to be distinguishable, grow harsher, then become slower, until when the interval of the octave is reached they also disappear. A great controversy with respect to these low tones of the grave harmonics has arisen in recent years, and though it smoulders from month to month, occasionally blazes up into vigorous flame. The controverted question is, What are these grave harmonics, and to what are they due? Also, What becomes of the beats when they occur so rapidly that the ear cannot distinguish them? The answer given by Dr. Thomas Young, and by Smith in his "Harmonics" (1749), was that the rapid beats actually passed into the grave harmonic, just as in the generation of any pure tone the separate vibrations (which, when continuous tone whose pitch depends upon their frevery slow, are heard as separate sounds) blend into one quency. This view is maintained at the present day with great energy also by the famous acoustician Dr. Rudolph König of Paris. On the other hand, Helmholtz has emphatically maintained that the grave harmonic is not, and cannot be, thus accounted for, and has given very cogent reasons for thinking that it has another explanation; and in this view he is supported by Preyer, Lord Rayleigh, Ellis, Bosanquet, and all the best English physicists. Mere alternations of sound and silence, however rapidly they occur, cannot produce the same effect on the mechanism of the ear as a pure to-and-fro motion of the same periodic frequency. A tuning-fork which vibrates 100 times per second will give out waves which, falling on the ear, push the drumskin in, and draw it back that number of times per second. But a continuous tone interrupted 100 times per second by short periods of silence produces quite à different mechanical action on the mechanism of the ear. The writer of this article once tried to ascertain, by the experiment of rotating a vibrating tuning-fork upon its axis, whether the alternations of sound and silence which are observed as it is rotated would blend into a continuous tone; but no kind of blending took place. Another most conclusive proof that the beats and the beat-tones are distinct phenomena is that at a |