80

60

The membrane itself is about this length, and th of an inch wide, tapering towards the proximal end. The smaller specimen is th of an inch in entire length, and th wide. If these young forms had not been in connection with a mature graptolite, they would have been considered to belong to the genus Diplograpsus, but it would have been impossible to refer them to any species. In their present position he thinks we may without hesitation infer that they are the young of the graptolite with which they are associated. That they have not yet entered upon independent existence we cannot conclude; for they are in different stages of growth, and young graptolites are frequently met with in a less advanced state than either; indeed, on the same piece of shale there are several young graptolites referable to the same species, and no more developed, some even less so.— Annals and Magazine of Nat. History, May.

When is a Blood Corpuscle in Focus?-Dr. Tyson has* a very interesting note, accompanied by a diagram, which we regret we cannot reproduce, on this optical and physiological subject. After explaining the diagram, he says it can easily be carried in the mind's eye, and at once the facts can be thought out without burdening with their recollection the memory, which is here peculiarly apt to be treacherous. Indeed, he said he could never himself promptly recall the circumstances under which the centre had been bright and the periphery dark, and vice versa, until he had called to his aid this diagram. And that the exact truth is liable at least to escape attention, is seen in the circumstance that "in a volume no less highly valued than the seventh edition of Carpenter's 'Human Physiology,' 1869, is contained a misstatement of the facts. We find here, on page 200, the statement that the corpuscle is rather beyond the focus of the microscope when the periphery is dark and the centre bright, and within the focus in the opposite appearance-that is, when the centre is dark and the periphery bright. The reverse is correct. In the last edition of Carpenter (1868) On the Microscope,' however (pages 166, 167), we find the principle applied, and the fact correctly stated, though a few lines farther we find it asserted that the hexagonal areola in diatoms appear dark when the surface is slightly beyond the focus, though they are described as hexagonal elevations. If this latter be the case, then they should appear dark when within the focus, as is the case with the periphery of the corpuscle. So, too, on page 710 of this latter volume there is reproduced the same drawing referred to in the textbook on physiology, but with the description reversed, and therefore correct. The corpuscle is, however, described as in focus when the periphery is in focus, whereas we have presumed that the entire corpuscle is in focus when there is least shadow. Of the other text-books now within our reach, Dalton has it correctly on page 214 of his third edition; Flint, Kirke, Ranke in his 'Grundzüge der Physiologie,' and Rollett in Stricker's Handbuch der Lehre von den Geweben,' refer to the reversal of light and shadow, but do not state the circumstances under which it takes place; Marshall makes no allusion to it."

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* Philadelphia 'Medical Times.'

Extraordinary Microscopy.-In a journal published in Philadelphia called the 'Medical Times,' which is remarkable for several able and interesting medical papers, we find an extraordinary communication (March No.) by Dr. Neulenz. The following quotation will give our readers some idea of this gentleman's opinions. We are a little surprised at their making their way to so great an extent as a column and a half in such a paper as the Medical Times':-" Having constructed a one-seventieth immersion objective, on a new principle, having 191° aperture, the immersion liquid being fluoric acid, and, for illumination, having invented a new eccentric parallelopiped, to be used with fluorescent rays exclusively, some remarkable results have been obtained. I take great pleasure in stating that, with regard to test-objects, all previous observers have been totally wrong in every particular, and that Pleurosigma angulatum is, in the first place, constructed on the plan of the Nicholson pavement, and, in the second place, that it is not a Pleurosigma at all. The most certain test-object is the Newlenzia difficilissima, a very rare and remarkable diatom, in which my one-seventieth with the parallelopiped shows four kinds of beads and six sets of cross-lines, one of which sets contains 147,229,073 lines to the inch: hence, by the d.x d. น

well-known formula of Brewster,

=

o.x.p.y, it is impossible

that the undulations of light should pass without being previously deflagrated, and therefore no other lens can possibly show these lines, nor is it probable that this lens would with any other observer. The immense superiority of this test to Nobert's plate is apparent."

The

Note on Amphipleura pellucida.-Assist.-Surgeon Woodward, who may be said fairly to take first rank among American microscopists, has contributed a paper on this subject to 'Silliman's American Journal' for May. He says the attention of microscopists has frequently been directed, of late years, to the Amphipleura pellucida or Navicula acus, as a test-object well suited to try the defining powers of the very best object-glasses. The length of this diatom is stated by Pritchard as ranging from 14th to th of an inch. average length is given by the 'Micrographic Dictionary' at 0044 of an inch. The striæ, which are exceedingly difficult, were first described by Messrs. Sollitt and Harrison, who estimated them at from 120,000 to 130,000 to the inch. Their estimate has been adopted by the 'Micrographic Dictionary' and by the majority of modern writers who have referred to this test; but so many difficulties beset the resolution that few microscopists appear to have attempted to verify the original estimates. Indeed, most observers would seem to have been unsuccessful in their efforts to resolve the Amphipleura even with the best objectives, and some have gone so far as to deny the existence of any striæ upon the frustules of this species. Among the microscopists who claim to have seen the striæ, several would seem to differ from the original estimates of Sollitt and Harrison as to their fineness. Dr. Royston-Pigott, whose papers on "high-power definition" in the 'Monthly Microscopical Journal' have

1000

recently attracted much attention, sets down their number at 150,000 to the inch. Dr. Carpenter, on the other hand, in the fourth edition of The Microscope and its Revelations,' expresses the opinion that even the estimates of Messrs. Sollitt and Harrison are too high: and we are told by Mr. Lobb (Monthly Microscopical Journal,' vol. iii., p. 104) that Mr. Lealand has recently "succeeded in counting the Amphipleura lines and finds them 100 in th of an inch. A few months ago two slides of Amphipleura pellucida were received at the Army Medical Museum from Messrs. Powell and Lealand, and he succeeded in obtaining excellent resolution by the immersionth of these makers. The frustules on the two slides were found to measure fromth to th of an inch in length. Resolution could be satisfactorily effected and the striæ counted on any of them. He took eight successful negatives from medium size and small frustules, and verified the counts made in the microscope by counting the striæ on the glass negatives. He found the striæ on medium-sized frustules, say 20th of an inch in length, counted usually from 90 to 93 striæ to the Tooth of an inch; in that selected for the two photographs which were sent to the editors, the number was 91 to the th of an inch. Larger frustules exhibited rather coarser, smaller ones rather finer striæ. On the smallest frustules at his disposal, several of them only 4th of an inch in length, he found no example in which the number of striæ exceeded 100 to the 10th of an inch. The striæ of these smallest and most difficult frustules do not then rival in fineness the nineteenth band of the Nobert's plate, as has been asserted by some; they compare rather with the sixteenth and seventeenth bands. After making the photographs, he extended his observations to a number of other slides of Amphipleura pellucida, including two of the original specimens from Hull, kindly sent to the Museum some time since by Mr. W. S. Sullivant, of Columbus, Ohio, and the example in the First Century of Eulenstein. He found that different slides varied considerably in the case with which he could resolve them, chiefly as he thinks on account of the thickness of the glass covers, which in several instances did not permit the best work of the immersionth. Perhaps, however, the markings on some frustules may be shallower than on others whose striæ count the same number to the Toth of an inch. In any event he has found, as yet, no slides the covers of which permit theth to be approximately adjusted, on which it was impossible to resolve the frustules, and no frustules the striae of which exceeded 100 to the Tooth of an inch. The best resolution he was able to obtain by ordinary lamplight was not very satisfactory. He used therefore, during the investigation, direct sunlight, rendered monochromatic by passage through the solution of ammonio-sulphate of copper. A parallel pencil of such light was concentrated by the achromatic condenser, which was suitably decentred to attain obliquity. The same illumination was employed in making the photographs. He has since had the pleasure of exhibiting the resolution in quite as satisfactory a manner to several microscopists by monochromatic light obtained from the electric lamp.

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NOTES AND MEMORANDA.

No Meeting of the Royal Microscopical Society this Month.-We beg to notice that, contrary to what has already appeared, there will be no meeting of the Royal Microscopical Society this month. It was intended to have held one, but the College being occupied on both the first and second Wednesdays in the month, the Council has been compelled to give way. Consequently, Fellows will observe that there will be no meeting of the Society held this month.

Contributions to the Journal.-We may state that various papers remain on hand. Among others, a long French communication, which cannot appear this month. We mention this fact to allay any anxiety which may be felt by persons who send contributions which do not immediately appear. We do our utmost in all cases to insert the articles which are sent to us, as well as the Reports of the local Societies; but of course cases occur wherein even for two or more numbers papers do not appear. We mention this fact merely to reassure our correspondents as to their communications.

CORRESPONDENCE.

TOLLES' STEREOSCOPIC BINOCULAR EYE-PIECE.

To the Editor of the Monthly Microscopical Journal.

HOBART COLLEGE, GENEVA, N.Y., U.S.

SIR,-I wish to correct as widely as possible a statement in regard to the stereoscopic binocular eye-piece, which attributes the invention to me instead of Mr. Tolles, to whom really the whole credit belongs. Dr. Carpenter has made, unintentionally, such a statement, and it has been copied by others.† I doubt not it will be rectified in future editions. This misstatement was unknown to me until within a few weeks. If it had been known I should have made the correction promptly. It is not difficult, perhaps, to account for the mistake, inasmuch as I first exhibited this eye-piece in England at the soirées of the Microscopical Society and the Royal Society, and to numerous individuals, among them Dr. Carpenter himself, who expressed his satisfaction at its performance. Mr. Ladd, the well-known philosophical instrument maker, 11 and 12, Beak Street, Regent Street, had it for some time in his possession, and indeed made one, which however was much inferior to Mr. Tolles', as Mr. Ladd had not time to determine the proper curves, if indeed the lenses were achromatics 'Microscope,' 4th ed., p. 35. + The Microscope,' by J. Hogg, 7th ed., p. 119.

*

6

at all. He understood, however, that it was Mr. Tolles' eye-piece; and I have by me the original "exhibitor's card" at one of the soirées named, reading distinctly, "Tolles' binocular eye-piece, exhibited by Prof. Smith." I feel very anxious to have the mistakes corrected.

Of

The first eye-piece of this form which Mr. Tolles ever made was purchased by me, and I gave some account of its performance and peculiarities in the American Journal of Science,' July 1864, p. 111. And, in the same journal shortly after, Mr. Tolles himself described its construction. Now, although we cannot expect everyone to read an American journal, or to be posted in all that is done this side of the Atlantic, even in the microscopical line (except to notice the trash, e. g. the mean little sheet issued by manufacturers and sellers of the Craig !!! microscope, recently attempted to be palmed off as the organ of the Illinois Microscopical Society), it is a little surprising, considering the length of time these two articles have been published in a most prominent journal, that such a blunder should occur. course it is inadvertence. Dr. Carpenter, I am quite sure, is ready and willing to do full justice, and in so doing it will be proper to state the real principle of the eye-piece in question. It is not, as he has stated, l. c., merely an arrangement of prisms similar to MM. Nachet's, for in reality the prime part of the eye-piece may be this, or Riddell's, or Wenham's; and, in fact, in the first eye-piece made for me was different from either of these. Mr. Tolles finally-partly at my suggestion, though I believe he had already decided upon it-adopted the Nachet form, and he claims nothing for this. What he does claim, and is justly entitled to claim, is the construction of a firstclass achromatic erecting eye-piece, and a division of the pencil, for stereoscopic vision, at, or very near, the point of crossing of the rays in such a combination. Now, it is well known that the difficulty in using the Wenham, or Nachet arrangement with high powers, arises from the necessity of dividing the pencil so far behind the objective, a difficulty which it seems cannot be got over, except upon Mr. Tolles' plan, viz. making a secondary image, and dividing the pencil here, or near the point of crossing of the rays. The binocular eyepieces invented by President Barnard, and by myself, are simply binocular, like Powell and Lealand's arrangement for high powers, though superior as to equality in illumination of the two fields, they are not stereoscopic. Perhaps the fact of my having made such an eye-piece, and published an account of it, as also Dr. Barnard's notice of it, in his report upon the Paris Exposition, may have assisted to mislead in attributing the really stereoscopic binocular of Mr. Tolles to me. I had been the originator of this eye-piece, which is yet destined to replace most binoculars, I should feel I had contributed a much greater boon to microscopy than anything I have yet done. The instrument, as made now by Mr. Tolles, is very perfect; the loss of light is trifling, easily remedied by a little more illumination. The loss in definition is not so much as in the Wenham and Nachet forms; not merely from the care with which Mr. Tolles works the prisms, but owing to the much shorter distance which the reflected ray has to travel. This part of Dr. Carpenter's objection is practically without

If