SCIENCE- G OSSIP. 



37 1 



CONDUCTED BY P. SHILLIXGTON SCALES, F.R.M.S. 



Royal Microscopical Society, March 20th. 

 Mr. A. D. Michael, vice-president, in the chair. — 

 The secretary called attention to an excellent 

 portrait of Peter Dollond, presented to the Society 

 by Mr. C. L. Curties. Mr. Nelson referred to two 

 old microscopes which had recently come into the 

 possession of the Society. The first — a non- 

 achromatic microscope — has the name of Carpenter, 

 24 Regent Street, engraved upon it, and its date 

 may be assigned to about 1825. It was especially 

 interesting from the fact that the late Hugh 

 Powell, before he began to make microscopes on 

 his own account, made them for the trade, and in 

 this instrument they doubtless had an early speci- 

 men of Hugh Powell's work. The other microscope, 

 of the Culpeper and Scarlet type, was signed 

 Dollond, and its date was probably not later than 

 1761. Messrs. Staley & Co. sent for exhibition a 

 Bausch and Lonib Camera Lucida, described in 

 the Journal last December. It was intended for 

 reproducing natural size an object diagramatically. 

 Mr. E. M. Nelson read a paper, " On the Working- 

 Aperture of Objectives for the Microscope," in 

 which he showed that in recording delicate obser- 

 vations it was advisable to state the precise ratio 

 of the utilised diameter of the objective to the full 

 available aperture. He then proceeded to explain 

 the different methods by which this ratio — which 

 he termed the working ratio, or W.R. — could be 

 measured. Dr. Tatham confirmed Mr. Nelson's views 

 in regard to the necessity for recording the working 

 aperture of objectives, and expressed his apprecia- 

 tion of the value of the methods proposed by the 

 author for obtaining this measurement. A paper 

 by Mr. H. G. Madan, F.C.S., "On a Method of 

 Increasing the Stability of Quinidine as a Mount- 

 ing Material," was read by Mr. Nelson in the 

 absence of the author. Mr. Madan found that by 

 keeping quinidine heated to a certain temperature 

 for a considerable time it was converted into colloid 

 quinidine, which condition it had retained for a 

 year, but whether the tendency to revert to the 

 crystalline form was entirely overcome time alone 

 could show. Mr. Karop said of all media, quini- 

 dine, on the whole, was the best yet discovered for 

 mounting diatoms, but was very troublesome on 

 account of its tendency to crystallisation. He 

 hoped the material, prepared as suggested by Mr. 

 Madan, would be offered for sale, when he would 

 give it a trial. Mr. Rousselet read a paper " On 

 some of the Rotifera of Natal," by the Hon. Thomas 

 Kirkman, illustrated by mounted specimens shown 

 under microscopes. Mr. Rousselet had appended 

 a technical description of Pterodina trilobata, one 

 of the rotifers mentioned in the paper, a mounted 

 specimen of which . was among those exhibited. 

 An excellent drawing of this rotifer by Mr. Dixon 

 Nuttall was also shown. Mr. W. H. Merrett read 

 a paper " On the Metallography of Iron and Steel," 

 demonstrating the subject by the exhibition of a 



large number of lantern slides of sections of dif- 

 ferent classes of these metals, under various con- 

 ditions of hardness, stress, etc. The methods by 

 which these sections had been prepared and 

 polished were also explained. 



Instantaneous Photomicrography.— Mr. A. 

 C. Scott, of Rhode Island College, has devised an 

 arrangement by which he has been able to obtain 

 instantaneous photographs of microscopic living 

 organisms. A powerful light is, of course, neces- 

 sary, and in his own work he has used an arc 

 light of 2,200 volts, giving about 4.000 candle- 

 power. This light is placed at a distance slightly 

 greater than the focal length of the condensing 

 lens to obviate such concentration of heat as 

 would be detrimental to the microscope objective. 

 The camera is of the usual vertical type, but the 

 important essential is a . combined shutter and 

 view-tube, which is clamped by means of three 

 thumb-screws to the draw-tube of the microscope : 

 this apparatus is fastened above the ocular, and 

 after the latter has been inserted in the draw-tube. 

 The mechanism of this apparatus is described by 

 Mr. Scott as follows : " Upon a movable brass 

 plate inside a light-tight box is a 90° prism, 

 mounted in such a way that all the light which 

 passes through the microscope is projected upon a 

 piece of ground glass at the end of a cone, which 

 may be lengthened or shortened in order to give 

 correct focus to the object, when it is properly 

 focussed upon the ground glass of the camera 

 directly above the microscope. Next to the prism 

 is a hole in the brass plate for allowing light to 

 pass from the microscope directly to the photo- 

 graphic plate, when the prism is moved by a spring 

 and pneumatic release, and finally a sufficient 

 area of the brass plate to cover the opening when 

 exposure has been made. To take a photograph, 

 the microscopic animal is placed in a drop of water 

 upon a suitable glass plate, the light is turned on 

 and the shutter so set that the object may be 

 focussed upon the ground glass of the cone. The 

 plate-holder is inserted and the dark slide drawn, 

 leaving the plate exposed inside the camera bellows. 

 The movements of the animals are easily seen upon 

 the ground glass, and when the desired position is 

 obtained the shutter is released, the prism moves 

 out of the way and the light passes to the plate." 

 The apparatus is not yet perfected to its inventor's 

 complete satisfaction, but he states that exposures 

 as short as one-fortieth of a second have been 

 very satisfactory, and considers that thoroughly 

 satisfactory negatives can be obtained with low- 

 power objectives in one-hundredth of a second. 

 The magnification has, however, ranged up to 200 

 diameters. Mr. Charles Baker, of High Holbora. 

 in his last catalogue, mentions a somewhat similar 

 arrangement for instantaneous photomicrography 

 in which a pneumatic shutter with a prism attach- 

 ment enables the object to be viewed on a ground- 

 glass screen at right angles to the optic axis up to 

 the moment of exposure. We have not. however, 

 seen this apparatus. Mr. Andrew Pringle. in his 

 well-known book on practical photomicrography. 

 describes a vertical camera for the -ame purpose, 

 but of different construction. This camera is fitted 

 with a pair of "goggles " and a velvet bag for the 

 head. An instantaneous shutter, made of thin sheet 

 aluminium, lies almost in the plane of the sensitive 

 plate and bears white discs upon which the focus- 

 sing is done, and the image watched until the time 

 for exposure. 



