276 



SCIENCE- GOSSIP. 



CONDUCTED BY F. SHILLIXGTOX SCALES, F.R.M.S. 



Eoyal Microscopical Society, December 18th. 

 — Wm. Carruthers, Esq., F.E.S., President, in the 

 chair. Messrs. R. & J. Beck exhibited a new micro- 

 meter microscope, the body of which was made to 

 traverse across a long stage by means of a fine 

 screw, the milled head of which was divided so as 

 to indicate a movement of ji^th millimetre. The 

 body could also be placed in a horizontal position, 

 when it could be used as a telescope to measure 

 distant objects. Mr. F. W. Watson Baker exhibited 

 a number of microscopic specimens illustrating the 

 development and structure of eyes. They were 

 shown under twenty microscopes, and were the 

 most perfect sections that could be obtained from 

 the best preparers in this country and abroad. 

 Mr. E. M. Nelson sent three notes, which in his 

 absence were read by the Secretary. The first was 

 a description of Holtzapffel's microscope. The 

 date of it is 1830, and in it are found four original 

 devices : (1) It possesses a clamp foot for clamp- 

 ing the instrument to the edge of a table, predating 

 a similar device of Varley's in 1831 ; (2) the back 

 of the mirror is flat polished brass, so that mono- 

 chromatic light may be reflected by it ; (3) the 

 stage is focussed by an eccentric which differs 

 from and predates the somewhat analogous devices 

 of Pacini and Plossl : (4) the movement of the 

 lens-holder is by means of a steel tape and 

 pinion. The second note was a description of 

 the first English achromatic objective, made 

 by W. Tulley. It was a triplet and was made 

 at the suggestion of Dr. C. R. Goring, who paid 

 £90 for it. The focus of the combination is 

 0-933 inch, initial magnifying power 10-72, 

 N.A. -259, and the O.I. the large" amount of 24 -2, 

 Mr. Nelson then described the Chevalier-Euler 

 achromatic objectives of 1823-24 and 1824-25. 

 These were doublets, and in 1827 Mr. J. J. Lister 

 put one of Chevalier's doublets as a front and 

 a Tulley's triplet as a back lens. The focus of 

 the combination was 0-52 inch : it was the finest 

 microscopic objective that had up to that time 

 been produced, and was. strictly speaking, the first 

 really successful scientific microscopic objective. 

 Lister's labours in perfecting objectives and the 

 great use they had been to the leading opticians of 

 the day were referred to. The third note was on 

 1; A Useful Caliper Gauge." It can be purchased 

 at any watchmaker's tool-shop for three or four 

 shillings, and is convenient for measuring the 

 thickness of cover-glasses, and for low-power work 

 the scale may be placed on the stage of a micro- 

 scope and the constant of an eyepiece micrometer 

 found by comparison with the mm. divisions. The 

 President gave an account of some investiga- 

 tions which he had made in reference to a disease 

 that had caused great mischief in cherry orchards 

 in Kent. About fourteen months ago, when 

 his attention was first called to it, the disease 

 was prevalent over a considerable area, a notice- 



able feature in connection with it being persistence 

 in the autumn of the dead leaves on the branches, 

 instead of then- falling off, as they would have done 

 if the trees were healthy. The leaves of affected 

 trees were pervaded by the mycelium of a fungus 

 which destroyed them, and as the food of the tree 

 was prepared by the leaves the growth of the tree 

 would in consequence be arrested. The results of 

 experiments in the cultivation of the fungus showed 

 it to be one which belonged to the genus Gnomonia. 

 Many of the fungi in this class passed through 

 various stages in their life history ; for example, 

 the mildew on wheat, which was first developed on 

 the berberry and then spread to the wheat, appear- 

 ing originally as rust, and afterwards as mildew, 

 from the same mycelium. The President referred 

 to the absence in this country of any author 

 competent to investigate cases such as this. On 

 the Continent, however, the Governments had taken 

 up the matter, and the experts who had examined 

 into it had found that to check the spread of the 

 disease it was necessary to collect all the dead 

 leaves and burn them. The President had conse- 

 quently urged upon the fruit-growers the necessity 

 of following this recommendation, but had only 

 been able to persuade two growers to do so. Both 

 of these, however, had found it to be thoroughly 

 effective. Professor A. W. Bennett in his remarks 

 enlarged upon the absence in this country of 

 investigations into such matters by State-paid esta- 

 blishments, and described what was being done in 

 the United States, where every State had its own 

 experimental station. The President announced 

 that the next meeting would be the annual meeting, 

 when the officers and council for the ensuing year 

 would have to be elected, the nominations for 

 which were then read. 



Quekett Microscopical Club. — Decem- 

 ber 20th. 1901, at 20 Hanover Square, W., the 

 Right Hon. Sir Ford North. F.R.S., F.R.M.S., in 

 the chair. Mr. Angus exhibited and described the 

 use of two simple apertometers. The first was an 

 ordinary semicircular protractor held at the middle 

 of its periphery vertical to the stage : at the centre 

 point was fixed a perforated film, mounted on 

 glass, parallel with the stage. Riders or pointers 

 slid along the arc, indicating the angle. The hole 

 in the film was focussed by the lens to be tested, 

 and the back of the lens examined with a low 

 power, as when the Abbe apertometer is employed. 

 The sine of half the angle indicated would be the 

 numerical aperture. This appliance was valueless 

 for measuring immersion objectives, as it onlv 

 measured 180° in air. The second apertometer 

 was merely a mm. scale placed in the turn-out 

 ring of the condenser. The condenser and an 

 objective of known aperture were focussed on the 

 same plane, and the N.A. value of a division in the 

 mm. scale was found by an examination of the 

 back lens of the objective. When any other 

 objective was employed the number of divisions 

 visible at the back lens, multiplied by the deter- 

 mined value of one division, gave the aperture of 

 the objective. Mr. Angus showed the value of 

 such a quick method of measuring aperture by the 

 ease with which the size of diaphragms and stops 

 could be found ; he also gave the proportions of 

 stops to apertures which furnished the best dark- 

 ground effects. Stops were shown that were made 

 of black paper gummed to glass discs, cut to fit 

 the condenser turn-out ring. The club's best 

 thanks were accorded to Mr. Angus for his ex- 



