LANG, Dr. A.-Communications on Microscopical Technic:-(1) A New Staining Method. [See this Journal, II., p. 163.] (2) Supplement to Note on the Preservation of Animals by a Sublimate Solution. [See this Journal, I., p. 256.] Zool. Anzeig., II., No. 19. LENZ, Dr. H.-Improvement in the Aerating Apparatus of Marine Aquaria. [See this Journal, II., No. 18.] Zool. Anzeig., II., No. 18. SEILER, Dr. C.-Practical Hints on Preparing and Mounting Animal Tissues (continued). Am. Q. Micr. Journ., I., No. 3. Sharpus's Method of Mounting Echinoderms and other Objects. Midl. Nat., II., No. 17. T. C.-A New Method of Preserving Infusoria. UNDERHILL, H. M. J.-The preparation of Insects for Microscopical Examination. [1st part] Sci.-Gossip, No. 173 DIPPEL, Prof. Dr. L.-Contributions to General Microscopy. I. Prof. Abbe's Apertometer. (2 figs.) II. The Objectives for "Homogeneous Immersion" of Carl Zeiss, of Jena. (16 figs.) Zeitschr. f. Mikr., II., No. 2. Am. Q. Micr. Jour., I., No. 3. HITCHCOCK, R.-Micrometry. HYDE, H. C.-Presidential Annual Address to the San Francisco Microscopical Society. Am. Journ. Micr., IV., No. 3. MALASSEZ, L.-Correction of the Distortions produced by the Camera Lucida of Milne-Edwards and of Nachet. (3 figs.) Trav. Lab. Histol. Coll. France, 1877–8. Note on the Measurement of Microscopic Amplifications. (1 fig.) Trav. Lab. Histol. Coll. France, 1877-8. Mayall, J., jun.-Immersion Illuminators for the Microscope. [Translation of paper read before the Brighton and Sussex Natural History Society.] Journ. de Micr., III., No. 4. PELLETAN, Dr. J.-New Laboratory Microscope. Journ. de Micr., III., No. 4. ROGERS, Prof. W. A.-On Two Forms of Comparators for Measures of Length. (1 fig.) Am. Q. Micr. Journ., I., No. 3. ROTATING CLIPS for Cheap Microscopes. (1 fig.) Am. Journ. Micr., IV., No. 4. Roy, C. S.-A New Microtome. (1 fig.) Journ Phys. (Foster). II., No. 1. RUTLEY, F.-An English Microscope for the use of Students of Mineralogy and Petrology. (1 fig.) [See this Journal, II., p. 471]. Nature, XX., No. 496. SIMPLE CONTRIVANCE for holding the Object beneath the Stage of the Microscope. (1 fig.) M. Journ. Sci., I., No. 65. SMITH, Prof. H. L.-A few Remarks on Angular Aperture, and Description of a "Universal Apertometer." (1 plate.) Am. Q. Micr. Journ., I., No. 3. SUB-STAGE for Oblique Light. (1 fig.) Am. Journ. Micr., IV., No. 4. TOLLES, R. B.-Clear Working Distance. (2 figs.) Journ. de Micr., III., No. 4. VORCE, C. M.-The Mechanical Finger. (1 fig.) Am. Journ. Micr., IV., No. 3. WARD, Dr. R. H.-On a Standard for Micrometry. Am. Nat., XIII, No. 5. WENHAM, F. H.-On the Formation of the Paraboloid as an Illuminator for the Microscope. (3 figs.) Am. Q. Micr. Journ., I., No. 3. Williams, W. M.-Spiders' Webs for Micrometers. (From 'Journal of the Society of Arts.') Am. Journ. Micr., IV., No. 4. PROCEEDINGS OF THE SOCIETY. MEETING OF 14TH MAY, 1879, AT KING'S COLLEGE, STRAND, W.C. THE PRESIDENT (DR. BEALE, F.R.S.) IN THE CHAIR. The President on taking the Chair congratulated the Fellows upon having obtained possession of their new room and upon the appearance it presented. They were very much indebted to the Library Committee for the successful manner in which they had arranged the room, and it was also satisfactory to know that this had been effected out of revenue, and without diminishing the capital account of the Society. The thanks of the Society were, on the motion of the President, voted to the Library Committee. The Minutes of the meeting of 9th April were read. Mr. Michael said that though Mr. Stephenson's motion included a declaration that the T of a millimetre was too large a standard, he and others who voted upon it understood that a suggestion of Dr. Edmunds had been adopted, and that the latter part of the motion only was intended to be put to the Meeting. Mr. Ingpen confirmed this, and The President, with the assent of the Meeting, erased the first part of the motion (leaving it to stand, "That in the opinion of this Society it is not expedient at present to prescribe by any formal resolution the adoption of a fixed standard for micrometry "), and the minutes were so confirmed and signed by the President. The List of Donations (exclusive of exchanges) received since the last meeting was submitted and the thanks of the Society given to the donors, viz.: Burgess, E.-The Anatomy of the Head and the Structure of the Maxilla in the Psocida. (Reprinted from the 'Proceedings of the Boston Society of Natural History.' Vol. xix. 1878) 'Index Medicus: a Monthly Classified Record of the Current Medical Literature of the World.' Compiled under the supervision of Dr. J. S. Billings and Dr. R. Fletcher. Vol. i. Nos. 1, 2, and 3 (January, February, and March.) 4to. New York, 1879 Trübner, N.-Bibliographical Guide to American Literature.' 8vo. London, 1859 12 Slides of Insects from Nevis, West Indies 15 Photographs of Blood-corpuscles of Man and Animals From The Author. The Editor. Mr. Crisp. The President, in reading the names of further Societies recommended by the Council under the bye-law as to Ex-officio Fellows, said that the Council had been much gratified at the extremely cordial manner in which the Societies previously nominated had received the nominations. Two of them had done him the honour to elect him an Honorary Fellow. Photographs (15) of blood, sent by Dr. J. B. Treadwell, of Boston, U.S. (through Mr. C. Stodder), were shown, and the following letter from Mr. Stodder read: "Dr. Treadwell's object is the measurement of the blood-disks and comparison of size of human blood with that of other animals, and the focussing is so done as to show the sharpest outline of the diameter. I will call the especial attention of the Society to those photographs on which there are two kinds of blood-blood from two animals. Several devices have been used by others to accomplish this object, one of much importance for obtaining in a picture the exact amplification for both kinds of blood, and which, I believe, has not been so successfully before accomplished. I trust that these will be acceptable to the Society. The mounting of the slides and the photographing is all done by Dr. Treadwell." Mr. A. W. Waters' paper "On the occurrence of recent Heteropora" (see p. 390), was read by Mr. Stewart, who also described by drawings on the black-board the slide of Membranipora membranacea brought by Mr. Dreyfus. Mr. John Davis's paper on "A new species of Cothurnia was read by Mr. Stewart, and the drawings enlarged on the board. Mr. Wenham's "Note on Homogeneous Immersion ObjectGlasses" was read by Mr. Crisp (see p. 394) : "From a paper contributed by me to the Monthly Microscopical Journal,' June 1st, 1870, I quote the following comments in favour of Homogeneous Immersion." 'One advantage in the immersion objective is that it almost prevents the loss of light from the reflection of the upper surface of the cover and front of lens, and in part neutralizes any error of figure and polish that may exist between them. There is also another condition annexed, it has the singular property of a front lens of adjustable thickness, and therefore can be set to the utmost nicety to balance the observations. Of course there is no optical advantage attendant upon the use of water. If a medium of the same refractive power as the glass were to be employed, the result would be better. Water having a low refractive index, an adjustment is required for each thickness of cover, and a difference of adjustment is not so marked and sensitive as in the ordinary dry objectives; but if a medium of similar refraction to the glass were to be used, no adjustment would be required for any thickness of cover, supposing the test objects to be mounted thereon (which they generally are), for in fact we should then view them all with a front of the same 2 к VOL. II. thickness-considering the cover, the front lens, and the interposing medium as one."" Mr. Stephenson being absent from town the following note from him was read by Mr. Crisp. "I have read Mr. Wenham's note containing a reference to his paper of 1870, of which, however, I was not aware when I brought the subject of Homogeneous Immersion before the Society in 1878. "I do not understand what it is that Mr. Wenham claims. "The use of oil instead of water was suggested by Amici prior to 1850; and it is equally clear that it was not until 1878 that any homogeneous immersion objectives were produced in a practical form, and then it was by Professor Abbe and Mr. Zeiss, and more recently by Messrs. Powell and Lealand. "As, during a great part of the period between 1870 and 1878, Mr. Wenham has been actively engaged in the construction of immersion object-glasses, it is evident that he did not appreciate the practical advantages likely to follow from the introduction of oilimmersion glasses any more than Amici and other previous experimenters on the subject did. "This is not surprising when it is remembered that the very essence of the homogeneous system depends under Professor Abbe's able development on an optical principle which Mr. Wenham has for many years contended, and still contends, to be a physical impossibility, viz. it gives an angle greatly in excess of even the ideal maximum of a dry lens (180°).* "Moreover, if Mr. Wenham had attempted to give practical effect to his suggestion of 1870 he would have found that identity of refractive index between the cover-glass and immersion fluid was by no means consistent with optical homogeneity, one of the most essential conditions of which is identity of dispersion." Mr. Wenham said that it had not been his intention to raise any controversy, but simply to record what he had done. If Amici had given a distinct description of it he did not, of course, want to claim it. Mr. Crisp said, that he thought it must be considered beyond dispute that Amici was the first to suggest and to use oil as an immersion fluid for objectives, in which he was followed by Oberhäuser, Harting, and others. They all apparently thought, however, that oil-immersion objectives, were not capable of practical application. He read the following extract from M. Robin's book: "We have seen that the principal obstacle to good resolution arises from the violent refraction which the rays undergo on leaving the cover-glass and passing into air, and again on their second refraction by the front lens. Amici thought that to correct this defect the front lens should form part of the cover-glass, but how could the distance of the object from the lens be made variable? Simply by interposing between them an elastic medium having nearly the same refractive index as the glass. He suggested that the lens * See 'M. M. J.,' v. pp. 16-17 and 118; vi. pp. 84-86 and 292; vii. p. 272; xi. p. 113; xii. p. 222; xiii. p. 35, &c. should be plunged in a liquid of the same index as the cover-glass, glycerine mixed with oil of aniseed, for instance, or even the latter alone; later he recognized that distilled water corrected very well the feeble aberrations produced by the differences in the relative thickness of the media, glass and water. . . . The experiments of Amici on immersion objectives date from 1844. I saw in that year, or the following one, at Oberhäuser's, an objective with which he showed the advantages [of the immersion system] by interposing between it and a preparation of Lepisma scales either a drop of neats' foot oil or a drop of essential oil. He considered them to be preferable to water, the employment of which he had already recommended as giving good results with all kinds of objectives of short focus." Mr. Woodall called attention to the passage in Professor Abbe's paper (see p. 256), in which he referred to Mr. Stephenson's suggestion, that homogeneous immersion objectives would allow of increased angular aperture, which suggestion led to the making of the objectives. -Mr. Ingpen thought they must all regret that Mr. Wenham had not followed up his experiments in homogeneous immersion. Had he done so, we probably should have long since had the oil-immersion objective as an English instead of a foreign production. The refractive index of the immersion fluid employed was not the only consideration-the selection of an oil of suitable dispersive power had been made by Professor Abbe, after many experiments. Moreover, it must be remembered that the great advantage of the oil lens was its increased angle and consequent augmented resolving power, which was not originally contemplated as a result of homogeneous immersion. In the case of the new lenses they had not merely the results of a series of experiments, but also their successful practical application in the construction of improved objectives. Mr. Wenham wished to say one word as to the medium. At the time referred to he had used oil of cloves. He did not care to make any oil lenses then because he had a wholesome fear of it. If the fingers were smeared with it and the instrument then touched, it took off the lacquer, besides unsetting the cement and destroying the objects. Mr. Hue's suggestion for the more convenient use of oil with homogeneous immersion objectives was explained by Mr. Crisp, viz. to screw over the front of the objective a small receptacle contain * Prof. Ch. Robin, 'Traité du Microscope.' Paris, 1871. Pp. 191–192. Prof. Harting, in his work on the Microscope, thus referred to the use of oil :— "If we could replace the layer of water by a fluid of still greater refractive power, such as oil, further advantages must obviously be obtained. This has been successfully tried. It seems to me, however, a great risk to bring costly objectives in contact with an oily fluid which would have to be again removed by alcohol and ether. This would be hazardous with double lenses cemented with Canada balsam. The immersion system has, it is true, been so arranged that the front lens is not a double, but a single one of crown glass, and for these immersion in oil would certainly be much less objectionable. Nevertheless, I must doubt whether the oil-immersion system can ever come into more general use."-P. Harting, 'Das Mikroskop' (2nd German edition). Brunswick, 1866. |