26 



Thanks were voted to the donors. 



Mr. Durham described a microscope designed by Mr. Marshall, President of 

 the Birmingham Natural History Society, and made by Mr. Field. It was 

 contained in a case which comprised a simple microscope with five or six powers, 

 with a cell for dissecting and pins for setting out an object. The dissecting 

 stage being removed, a mounting plate was put in its place with a contrivance 

 for centering and a turntable. The case also contained a tray, with mounting 

 materials and slides, and a drawer with dissecting implements. A tube or 

 body could be attached , so as to convert the instrument into a compound 

 microscope with a good achromatic combination, and also other apparatus ; 

 the price of the whole being £3 10s . 



Mr. Durham also read a letter from Mr. Tomlinson, calling the attention of 

 members to the motions of particles of Camphor. It was said that small 

 fragments of camphor would rotate if placed on any smooth, clean, solid 

 surface, and that the motion might be seen under the microscope; members 

 were invited to repeat the experiment, and communicate the results to Prof. 

 Tomlinson for publication. 



The President announced that the four gentlemen proposed at the last meet- 

 ing had been ballotted for, and elected members of the Club. 



Mr. Hislop read a description of a new simple Selenite Stage. 



Mr. M. C. Cooke read the translation of a paper by Count A. F. Castracane, 

 " On Micrometric Measurement." 



Dr. Matthews pointed out that in measuring by the aid of the Camera Lucida, 

 the amount of light diminishes as the object is enlarged, and that a different 

 calculation is required for each eyepiece and objective used. As to diatom 

 markings, they were variable even in different parts of the same valve ; with 

 cobwebs also it was difficult to say where to begin the measurement. 



Mr. Lowne had made all his measurements with the Camera Lucida, makinga 

 scale from the stage micrometer, and always using the same objectives and 

 eyepieces, and the same distances from the paper. There were, however, one 

 or two little points which required some attention, and which every novice 

 finds a matter of extreme difficulty, because he does not get a due balance of 

 light between the object and the paper. By using a reflected light from the 

 plane mirror for the object, and a direct light from a lamp for the paper, ad- 

 justed according to the requirements of the object, there would be no trouble 

 in the matter. For all rough measurements it was far the best method, though 

 for diatoms it might be necessary to use something more delicate, but no 

 difficulty would be experienced in camera lucida measurements down to 100 

 diameters. 



Mr. Breese had found that the ordinary Beale's neutral tint reflector, with a 

 micrometer on the stage, would give measurements as approximate as were re- 

 quired for all ordinary purposes. The method proposed by Dr. Matthews 

 would give as good results as anything, with fine measurements, provided that 

 one of the points were moved by a tangent screw. 



Dr. Matthews said that he had mentioned in his paper that the handles of 

 his micrometer might be worked by tangent screws j these had since been added, 

 and leave nothing to be desired. In using high powers it is a matter of great 

 importance to have perfect steadiness, and when a tangent screw is used the 

 motion is as delicate as could be wished ; it was not necessary to have a tangent 

 screw to both points. He should be happy to show the instrument again with 

 this improvement added. 



