April 14, 1892] 



NATURE 



575 



communication had been received from Prof. Czapski, "On the 

 Calculable Limit of Microscopic Vision." Its purpose was to show 

 why it was that great numerical aperture was of such high value 

 in the determination of minute structure, and to inquire whether 

 — seeing that a numerical aperture of I 60 was so utterly un- 

 available in the case of living objects, or of such as did not 

 admit of being put into media of sufficiently high refractive 

 index— there was any method of making these high numerical 

 apertures available for such objects ? The author had inquired 

 into the value of monochromaiic light for such a purpose, and the 

 latter part of his paper was to show that by using the blue rays 

 of such light with large apertures it was possible to increase the 

 aperture so as to obtain the relatively great advantage which 

 would result from a difference between I "40 and 175. Mr. F. 

 Crisp thought it should be pointed out that the broad fact dealt 

 with in this paper was one which had long ago been explained. 

 Dr. Dallinger said he had himself worked it out some time 

 ago, obtaining as a result the difference between I '40 and 170 

 which came remarkably near to that mentioned in the paper. 

 Mr. Crisp said that the aperture table which was printed with 

 every number of the Journal gave them the difference in resolv- 

 ing power between white light and monochromatic blue light 

 with objectives of various apertures. — Prof. F. Jeffrey Bell gave 

 an outline of the contents of a paper by Mr. H. L. Brevoort, 

 entitled "Observations on the Brownian Movement," and 

 pointed out that, whilst the general conclusion arrived at by the 

 author was that light had some influence in the matter, he did 

 not seem to have taken any precautions as to temperature, an 

 element which was usually considered to be an active agent in 

 this phenomenon. — A letter from the Hon. J. G. P. Vereker was 

 read, replying to some points raised during the recent discussion 

 of his paper "On the Resolution of Podtira Scales," — Dr. A. 

 C. Mercer read a paper on photomicrography as illustrated by 

 a collection of seventy- three lantern-slides. Among the slides 

 exhibited was a group which threw light on the vexed question 

 of Podura scale structure. The author showed conclusively that 

 the so-called featherlets on Podura scales are only inflations of 

 the membrane. A number of slides also proved the value of 

 the microscope as a means of detection in cases of forgery, or 

 when alterations were alleged to have been made in promissory 

 notes, the evidence afforded in one important case being very 

 clearly demonstrated. A further group of slides was devoted to 

 the illustration of the apparatus used in photomicrography. 

 The President, in proposing a vote of thanks to Dr. Mercer, said 

 he regarded the exhibition as the finest examples of what could 

 be done by means of photomicrography. 



Entomological Society, March 23.— Dr. D. Sharp, F.R.S., 

 Vice-President, in the chair. — The Secretary read a letter from 

 the City of London Entomological and Natural History Society 

 on the subject of a proposed Catalogue of the Fauna of the 

 London District. — Mr. G. C. Champion exhibited a number of 

 new species of Longicornia from Mexico and Central America, 

 recently described by the late Mr. H. W. Bates, in his paper 

 entitled " Additions to the Longicornia of Mexico and Central 

 America, with remarks on some previously recorded Species," 

 read at the last meeting of the Society. — Mr. S. Stevens ex- 

 hibited three very rare species of Noctuce, viz. Noctua flam- 

 matra, Leucania vitellina, and Laphygma exigua, all taken by 

 Mr. H. Rogers at Freshwater, Isle of Wight, in the autumn of 

 1891. — Mr. F. C. Adams again exhibited the specimen of Tele- 

 phorus rusticus, in which the left mesothoracic leg consisted of 

 three distinct femora, tibiae, and tarsi, originating from a single 

 coxa, which he had shown at the meeting on the 24th of Feb- 

 ruary last. The specimen was now reversed, to admit of the 

 better examination of the structural peculiarities of the leg, 

 upon which Dr. Sharp, Mr. Champion, and Mr. Jacoby made 

 some remarks. — Mr. Osbert Salvin, F.R.S., exhibited a series 

 of mounted specimens of the clasping organs in the male of 

 several species of Hesperidce. — Dr. Sharp exhibited, for Mr. 

 F. D. Godman, F. R.S., a collection of Orthoptera recently 

 made in the Island of St. Vincent, West Indies, by Mr. H. H. 

 Smith, the naturalist sent jto that island by Mr. Godman in 

 connection with the operations of the Committee appointed by 

 the British Association and the Royal Society for the investi- 

 gation of the Fauna and Flora of the Lesser Antilles. It was 

 stated that the collection had recently been referred to, and 

 reported on by, Herr C. Brunner von Wattenwyl and Prof, 

 J, Redtenbacher. — Mr. J, W. Tutt exhibited and remarked on 

 a series of various forms of Orrhodia vaccinii and 0. {spadicea) 

 ligula. — Mr. C. G. Barrett exhibited and made remarks on a 



series of specimens — including some remarkable varieties^-of 

 Bombyx qitercus and Odonestis potatoria. A long discussion 

 ensued as to the probable causes of the variation exemplified, 

 in which Mr. Tutt, Mr. E. B. Poulton, F.R.S., Mr. H. Goss, 

 Mr. Jacoby, Mr. Salvin, F.R.S., Mr. Bethune- Baker, Dr. Sharp, 

 and Mr. Distant took part. — Mr. G. A. J, Rothney sent for exhi- 

 bition a number of specimens of Camponotus compressus, C. 

 micans, CEcophila smaragdina, Sima rufo-nigra, Solenopsis gemi- 

 nata var. armata, and other species of Ants, from Calcutta. 

 He also communicated a short paper on the subject, entitled 

 " Notes on certain species of Calcutta Ants and their habits 

 of life." 



Paris. 

 Academy of Sciences, April 4. — M. d'Abbadie in the 

 chair. — Notice of the works of the late M. de Caligny, by M. J, 

 Boussinesq. — On certain systems of equations with partial differ- 

 entials, by M. Emile Picard. — Delivery from circular orifices, 

 and reappearance between their different superficial elements, 

 by M. J. Boussinesq. — On the native iron of Cafion Diablo, 

 Arizona, by M. Mallard. The author has examined some speci- 

 mens of native iron found in Arizona, the origin of which is 

 doubtful. The iron contains only 3 percent, of nickel, and when 

 polished shows cavities filled with a black substance supposed to 

 be iron carbide. In this comparatively soft substance a diamond, 

 o'5 mm. in diameter, was found by Prof. Koenig in 1890. The 

 iron appears to be of meteoric origin, judging from its appear- 

 ance. Mr. Foote has pointed out that the existence of a singular 

 elevation, called Crater Mountain, near the place where large 

 fragments of the material were found, may have something to do 

 with their occurrence, but he has been unable to find any volcanic 

 rocks in the neighbourhood. So the question of origin remains 

 sub judice, and a critical examination of the region will have to 

 be made before it can be settled. — On the spark spectra of gal- 

 lium, by M. Lecoq de Boisbaudran. The spectrum given when 

 sparks from a large induction coil play upon the surface of gallium 

 chloride consists of two characteristic violet lines, and a wide, 

 nebulous band in the green. If the same coil is used with a 

 condenser and metallic gallium, a much more complex spectrum 

 is obtained, and one from which the band in the green (wave- 

 length = 502-33) is absent. The two lines in the violet (wave- 

 lengths 4I7'04 and 403*19) are bright under both conditions of 

 sparking. Substituting a small coil for the large one, M. Lecoq 

 de Boisbaudran found that, besides the two violet lines, two 

 others, at the approximate wave-lengths 64i'24 and 639'23, 

 were seen when no condenser was employed. On introducing 

 the condenser, the latter line suffers a considerable diminution 

 in intensity. Another line occurs at X 632'67, and a nebulous 

 line about A. 535 "Si. The wave-lengths and characters of all 

 the lines observed under the three conditions are stated in detail. 

 — On a method for the determination of the mechanical ele- 

 ments of helical propellers, by M. S. Drzewiecki. — Observa- 

 tions of Swift's comet {a 1892), made at the Paris Observatory 

 with the West Tower equatorial, by M. G. Bigourdan. Obser- 

 vations for position were made on March 29, 30, 31, and April 

 I, 2, 3, 4. — The two asteroids discovered respectively by Wolf 

 on March 28, and Charlois on April i, were observed 

 for position by Mdlle. Klumpke, at the Paris Observa- 

 tory, on March 31 and April i and 2. — Observations of 

 Swift's comet (1892, March 6), made at Lyons Observatory, 

 by M. G. Le Cadet. Position observations were made on 

 March 31 and April I. — On the indices of refraction of saline 

 solutions, by M. Paul Bary. — New unipolar conductivity of 

 gases, by M. Edouard Branly. — On the attraction between 

 two disks separated by a dielectric, by M. Julien Lefevre. The 

 author has measured the attraction between two electrified disks 

 separated by a dielectric not in intimate contact with them, and 

 finds it to be represented by the following formula : — 



where F' equals the attraction stress between the plates at the 

 distance <• -f- if' in air ; F the attraction at the same distance 

 when a lamina whose dielectric constant is k, thickness e, and 

 having parallel faces, is placed between the plates ; ^ therefore 

 represents the sum of the thickness of air between the lamina 

 and the electrified disks. — On the production, in the dry way, 

 of some anhydrous crystallized sulphates, by M. P. Klobb. 

 (See Notes.) — On a nitroketone derived from campho- 

 sulphophenol, by M. P. Cazeneuve.— On the composition 



NO. II72, VOL. 45] 



