244 



SCIENCE- GOSSIP. 



CONDUCTED BY P. SHILLINGTON SCALES, F.K.M.S. 



Royal Microscopical Society. — On November 

 21st, Mr. Wm. Carruthers, F.R.S., President, in the 

 Chair. Mr. Nelson exhibited and described an 

 erect-image dissecting microscope by Leitz, sent 

 for exhibition by Mr. C. Baker, figured on page 509 

 of the Journal, August 1900. The erection of 

 the microscopic image, effected by means of Porro 

 prisms, was first described by Behrens in the 

 Journal of the Society in 1888. This instrument was 

 valuable as a dissecting microscope ; it was pro- 

 vided with hand-rests and three objectives having 

 a very long working distance. Mr. Disney ex- 

 hibited a diffraction plate, having the lines ruled 

 in concentric circles, by which the diffraction 

 bands were separated with great clearness. The 

 rulings were about 7,000 to the inch. He also ex- 

 hibited a steel brooch, the surface of which had 

 been ruled in the same way. The method by which 

 the lines were produced was at present a secret. 

 The articles were of English manufacture, and had 

 been lent to him by Messrs. Townson and Mercer. 

 Mr. C. F. Rousselet exhibited an electric lamp for 

 use with the microscope. After six months' trial 

 he had found it very satisfactory for work with 

 low and medium powers. It was manufactured by 

 Edison Swan Co., and was called the "Focus" 

 lamp. The President called attention to the ex- 

 hibition that evening of a number of slides from 

 the Society's Cabinet, prepared by the late Dr. 

 Carpenter in connection with his investigations 

 into the shells of the mollusca. Mr. B. B. Wood- 

 ward, who has given much attention to this subject, 

 had also brought down some valuable preparations 

 for exhibition. Mr. Vezey, at the request of the 

 President, read a short abstract, copied from the 

 Report of the British Association for 1846, which 

 was a resume of the original communication on 

 shell structure made to that Association by the 

 late Dr. Carpenter, to illustrate which the slides 

 exhibited were prepared. The President then called 

 upon Professor Charles Stewart, who, having re- 

 ferred to the views held upon shell structure at the 

 present day, and taking the common pinna shell as 

 an example, proceeded by the aid of drawings on 

 the blackboard to demonstrate how its structure 

 was built. Besides studying the sections usually 

 made, he recommended that the shells should be 

 broken and the fractured surfaces examined, if a 

 correct idea of the formation of the shells was to 

 be obtained. 



Freshwater Entomostraca.— Mr. D. J. Scour- 

 field, in the Proceedings of the South London 

 Entomological and Natural History Society, calls 

 att ention to the value of Entomostraca in experi- 

 mental biology. "Their commonness in all parts 

 of the country, their transparency, the ease with 

 which they can be isolated and reared under all 

 sorts of conditions, . . . mark out the Entomostraca 

 as particularly well fitted for observation in con- 

 nection with even the most fundamental biological 



problems of the day." He adds : " We badly want 

 detailed studies on local faunas, on the seasonal 

 distribution and variation of different species, on 

 the faunas of various types of ponds, on the food 

 of the most abundant forms, and many similar 

 subjects." 



J. Swift & Son's Condensers,— Messrs. J. 

 Swift & Son have submitted for our inspection 

 two excellent condensers of their manufacture. 

 The first is apo-chromatic, and has a numerical 

 aperture of -95. Its aplanatic aperture exceeds, 

 however, according to our measurements, -90 ; and 

 as the value of a condenser for anything approach- 

 ing critical work depends on the aplanatic cone of 

 light that it transmits, it will be seen that this 

 condenser is eminently fitted for such work. As 

 an apo-chromatic system it is, of course, distinctly 

 freer from colour than even the best achromatic 

 system can be made, and this is very manifest 

 when using high-angled lenses. The power is 

 about one-third of an inch, and the price, without 

 mount, £4 15s. We can recommend this con- 

 denser for all high-power work, and it is of 

 interest to remember that, so far as we are 

 aware, Messrs. Swift & Son share with Messrs. 

 Powell & Lealand the distinction of being the 

 only makers of apo-chromatic condensers through- 

 out the world. The second condenser is achro- 

 matic, and is an oil-immersion with a numerical 

 aperture of 1-4 and an aplanatic cone that we 

 estimate as exceeding 1-3. The corrections of this 

 condenser are also excellent, and the working 

 distance is ample, even with a thick slide. The 



Fig. 1. Apo- Condenser. 



Fig. 2. Oil Condenser. 



power is about |-inch, or |-inch with the front 

 lens removed, and the price without mount is £4. 

 Both condensers are constructed with the newer 

 makes of glass manufactured in Jena. It says 

 much for the enterprise, and perhaps the keen 

 competition, of our English opticians that we 

 should have been able to notice in these columns 

 within a short period three different immersion 

 condensers of high excellency by three leading 

 makers. 



Bausch & Lomb's New Catalogue. — What- 

 ever may be the respective merits of English 

 microscopes and lenses, as compared with those 

 manufactured abroad, there can be no question as 

 to the superior nature of the catalogues issued by 

 our foreign competitors. Messrs. Bausch & Lomb 

 have just sent us their new catalogue, which is a 

 large and handsome book of 186 pages, profusely 

 illustrated, excellently arranged, and strongly 

 bound in cloth. The copy sent us is numbered 

 6360 ! We hope shortly to give a brief notice of 

 some of Messrs. Bausch & Lomb's instruments and 

 apparatus, as this firm is now directly represented 

 in England. In the meantime the American 

 prices would scarcely serve for the English 

 market, an apo-chromatic ^-inch oil-immersion 



