facts in a good logical order, and introducing as little as possible that cannot be immediately explained. Many works are bad because their arrangement is muddling, and others are mischievous because their attempts at explanation continually suggest erroneous ideas. Mr. Barff's experience in teaching, under Professor Williamson, at University College, has enabled him to avoid these errors, and we are glad to see that he has had the courage to depart from the common plan of pestering his pupils with atomic weights and symbols before they can possibly know what they really mean.

The present work begins with simple explanations of chemical action, density of bodies, weights, measures, etc. Then follow chapters on hydrogen, oxygen, nitrogen, carbon, and their compounds, after which, chlorine, bromine, iodine, fluorine, sulphur, phosphorous, boron, and silicon are treated of, and conclude the first part. This first part having laid a good foundation of fact and experiment, the second part introduces chemical theory, and resumes subjects introduced in the first part, carrying the information further, and employing symbols, molecular weights, etc.

A student at the beginning of his career, is always puzzled by speaking of atomic weights as abstractions. Mr. Barff, therefore, in his first part, deals with absolute quantities in grammes and litres, selected in proportions. which lead up to the atomic and molecular weights subsequently mentioned. By this means the progress of the pupil is greatly facilitated, and unintelligent cram effectually stopped. At the close of each chapter in the first part, a number of questions are given, to which answers are appended. This is a valuable feature in the scheme, and, though not new, is better carried out than we recollect in any former book. At the end of the second part there is another series of questions and answers, the latter exhibiting in detail the mode of making all the calculations required. The book concludes with advice to candidates under examination, and a list of questions on chemistry in London University examination papers (matriculation), from January, 1865, to January, 1869, with the answers worked out.

We believe Mr. Barff's is the first book in which the new nomenclature is strictly adhered to, and this is of more consequence than at first appears, for although in many cases the choice between the new and the old name is simply a matter of convenience, yet cases frequently occur in which the latter names suggest opinions no longer deemed correct. Like all chemists, Mr. Barff finds himself in difficulty with the old terms, acids, bases, and salts. If all the things called acids, are examined, it will be found impracticable to tell what an acid is, and as things which possess properties opposite to acids, they properly defined while no definition can be given of the latter. "Salts" are equally troublesome, and, before long, it may be hoped no names will be used which have such fluctuating and variable senses.

bases are cannot be

It

is bewildering to call things which are not sour, "acid;" to denote as "salts," things soluble and insoluble, acid, alkaline, or neutral, as respects vegetable blues. Mr. Barff has made the best of these matters, and certainly, no elementary work on chemistry teaches so much in so simple a way. Knowing how difficult it is to get good books into schools, we must congratulate the University school for its good sense in adopting this work as soon as it appeared.

NOTES AND MEMORANDA.

NEW DIRECT VISION SPECTROSCOPE. At the soirée of the Royal Society, Mr. Browning exhibited a direct vision spectroscope, small enough to be carried in the pocket, yet so powerful, that it shows the D lines widely separated. The instrument contained ten prisms; four of these were of the great specific gravity 4.5. This is the densest glass that has been made for optical use in England. Although it contains a great quantity of lead, it seems to preserve a good surface. But in Mr. Browning's arrangement of the prisms the oxidizable surfaces are so completely protected from the action of the atmosphere, that the spectroscope might be used in a chemical laboratory. THE TRANSIT OF VENUS AND THE ASTRONOMER ROYAL.-Mr. Proctor has been engaged in some investigations which impugn the accuracy of the Astronomer Royal, who stated that the transit of 1874 is useless, so far as the mode of observation applied to the transit of 1769 is concerned, and suggested a mode of observation less perfect in itself, requiring many precautions, and little to be affected by chronometer errors. Mr. Proctor affirms that the transit of 1874, so far from being useless as respects the simpler mode of observation, is more valuable than the transit of 1882. If Mr. Proctor is right, the Astronomer Royal has been led into error by adopting an unsound method of testing the value of particular transits. We understand that Mr. Proctor has sent a paper on this subject to the Royal Astronomical Society, and, as some of the first mathematicians belong to that learned body, their decision as to who is right will be looked for with interest.

MUSICAL INTERVALS.-Several papers on this subject have lately come before the French Academy. One of the most interesting is by MM. A. Cornu and E. Mercadier, in which they come to the conclusion that a single scale will not satisfy all conditions. They affirm that the intervals in a scale of a melody are not precisely the same as in a scale of harmony. They remark that sounds that are pleasing in succession as melodies are not necessarily pleasing when superposed as harmonies, and we may even be astonished that the octave, the fifth, and the fourth do satisfy both conditions. The ear is most exacting when listening to melody only. In harmony, the volume of tone has also much to do with the variations from exact scales, that are permissible, because agreeable. Mr. Evans, the maker of the most perfectly tuned and voiced harmoniums, tells us that powerful organs cover up discords that are intolerable in instruments which yield only a small volume of tone.

THE LAND LEECH, Trochata subviridis.-Some interesting correspondence has been published in "Land and Water," proving that the above leech is a native of this country, as Dr. Gray affirmed in 1850. Some specimens, sent by a correspondent, were recently examined by Mr. Henry Lee, who identified them with the Trochata subviridis of Dubochet. He showed them to Dr. Baird and the Rev. W. Houghton, by whom the

identification was confirmed. When Dr. Baird put some of them into strong spirits, the colour left them, and gave a fine green hue to the fluid. Mr. Houghton shows that Dubochet considered them entirely terrestrial, while Moquin Tandon asserts that he kept them alive in water for more than fifteen days. Mr. Houghton says that neither of the individuals sent to him seemed at all at home when placed in water.

ANTIDOTE TO PHOSPHORUS POISONING.-M. J. Personne states, in "Comptes Rendus," that spirits of turpentine acts as an antidote to phosphorus. He considers it to have the property of arresting the action of phosphorus in depriving the blood of its oxygen, and thus causing death if the dose is large, or fatty degeneration, if small. He states, on the authority of M. Ambroise Tardieu, that French criminal statistics show that phosphorus has taken the place of arsenic as a popular poison, and that this has arisen from its employment in matches, and in the form of paste, to destroy noxious creatures. He refers to a statement of Dr. Letheby, that in an English lucifer factory the workmen are protected against the fumes of phosphorus by carrying small open vessels of turpentine on their breasts, so that the vapours of that substance are constantly inhaled. M. Personne's experiments were made on dogs, and were successful in eight cases out of ten, in which poisonous doses had been administered.

DEVELOPMENT OF SKULL IN DOMESTIC FOWL.-Mr. Kitchen Parker has brought this subject before the Royal Society, in a valuable paper, in which he says, "The multiplicity of parts in the bird's skull at certain stages very accurately represents what is persistent in the fish, in the reptile, and to some degree in certain mammals, but the skull at first is as simple as that of a lamprey or a shark, and in the bird, above all other vertebrates, reverts in adult age to its primordial simplicity, all, or nearly all, its metamorphic changes having vanished, and left no trace behind them."

FLUID CAVITIES IN MINERALS.-" Proc. Roy. Soc.," No. 109, contains an important paper by Messrs. Sorby and Butler, on fluid cavities in rubies, sapphires, diamonds, etc. A specimen of sapphire, of which they speak, exhibits a remarkable cavity, containing a fluid which appears to be liquid carbonic acid. They said of this fluid, "Though the expansion below 30° (Cent.) was very great, compared with that of any other known substances, except liquid carbonic acid and nitrous oxide, when the temperature rose above 30° (C.), it was so very extraordinary, that it was not until after having performed the experiment over and over again that Mr. Sorby felt confidence in the results." They found the expansion 780 times as much as that of water would be, and 69 times as much as air and permanent gases. Above 32° (C.) the fluid quite filled the cavity, so that its further expansion could not be ascertained.

HEAT OF THE STARS.-Mr. Huggins has laid before the Royal Society (in "Proc.") experiments made with his 8-inch refractor and a delicate thermopile, on the heat of stars. He obtained deflections of the needle with Arcturus 3° in fifteen minutes; Sirius 2°; no effect from Castor; Regulus 3°.

CORALS AND THEIR POLYPES.

BY P. MARTIN DUNCAN, M.B. LOND., F.R.S.,

Fellow of and Secretary to the Geological Society.

PART II.

(With a Coloured Plate.)

THE gastric and perigastric cavities of the majority of the Actinozoa are limited, inferiorly, by the membrane which covers the inside of the base, and they are not subdivided by any tissues which interfere with their continuity from the under surface of the tentacular disc downwards to the base. In the minority of the Madreporaria this is also the case, and when the soft parts of the corals have been washed away, the radiating septa bound spaces-interseptal spaces, or interloculi, which are open from the inner base of the corallum to the calice. The fleshy polypous covering of the Gorgonides and Antipatharia forms a more or less elaborate tubular water system on which the bases of the polypes rest, so that a section of one of them presents at its inner base the radiating foundation of the mesenteric folds and the water tubules. The hard stems of these last-mentioned corals do not receive the polypes into cavities within them, as is the case in the branching Madreporaria, and consequently there are never any sclerenchymatous processes which limit the great internal cavities of such types as Corallium and Gerardia.

But in the great majority of the Madreporaria, the continuity of the great cavities is constantly being interfered with during the upward growth of the polype, and its stony sclerenchyma. Such a corallite (as the term is in the case of aggregations, or corallum in the case of a simple form) grows by the deposition of new matter on the top of the septa, the wall, and costa, the most superficial of the hard parts; and the length of the perivisceral cavities, and the depth of the interseptal loculi increase with the growth. The growth above is, however, compensated by a shortening of the length of the great cavities below, so that however rapidly a corallite may assimilate the carbonate of lime for its flourishing sclerenchyma, and may elongate, the length of the mesenteric folds, and the depth of the visceral and perivisceral cavities always remain much the same. Coincident with the growth above is the occurrence of a series of projections of the inner tissue from the wall and sides of the septa

VOL. III.NO. IV.

R

a little above the base. The sclerenchyma passes into these projections which may be arched, or straight, or both. As these processes grow towards the median line, they close in a space which is of course quite shut off from the general cavities above when the projections between all the septa meet. The simplest form of these shutting-off growths is quite horizontal, and is called a tabula. Tabulæ pass quite across from one side of the inner part of the coral to the other, completely shutting-off a space. They occur in series one over the other, so that a tall corallum may contain many compartments one over the other. The curved processes are called dissepiments, and they occur in superimposed series so as to give a cellular appearance to longitudinal sections of corals. The tabulæ and dissepiments constitute the endotheca, are developed by the innermost layer of soft tissue, and they lose this covering inferiorly when the space they bound above is closed. The whole of this space loses its soft tissues, and as space after space is superimposed, so does all the coral below the uppermost dissepiment, or tabula die. As the endotheca is developed, the mesenteric folds are raised, for the lower surface of the tentaculiferous disc is elevated at the same time in consequence of the growth of the septa. The upper surface of the uppermost dissepiment, or tabula, forms the floor of the visceral and perivisceral cavities just as in other corals which have no endotheca, the inner part of the base fulfils this duty. On the outside of the Madreporaria, which develope endotheca internally, there is a corresponding structure between the external prolongations of the septa,-the costa, called the exotheca. It happens very generally, but not universally, that an exothecal projection on a level with an internal dissepiment limits the downward growth of the soft tissues externally, so that the extent of the internal and external soft tissues is regulated. They cease at a certain definite line, and all the hard tissues below it are extra-vascular and dead. In rapidly-growing Madreporaria very little of the great mass of the corallum is really alive, and the soft tissues only reach down internally and externally a few lines. I shall recur to this part of my subject, but it is necessary to observe that the limitation in depth of the mesenteric folds is compensated by a regular increase in their number by the formation of septa, and consequently of interseptal loculi, for most Madreporaria increase in diameter as they grow in length. As has been already noticed, each interlocular or interseptal space contains a mesentery which is attached close to the under part of the disc, is free below, or attached to the tissue covering the endotheca, or the true base, and free