59 



May 24th, 1872.^ — Chairman, Dr. R. Braithwate, F.L.S., &c., 

 Vice-President. 



The following donations to the Club were announced : — 



*' The Monthly MicroscopicalJournal " from the Publisher. 



" Science Gossip " the Publisher. 



" Proceedings of the Eoyal Society," Nos. 132-3 ... the Society. 



'* The American Naturalist," for March and April in Exchange. 



" Proceedings of the Geologists' Association" ... the Association. 



" Proceedings of the Literary and Philosophical") the Society 



Society of Manchester," for March and April J 



"The Lens" in Exchange. 



" The Journal of the London Institution " the Librarian. 



" The President's Address and the Reports, &c., of a 



the West Kent Natural History, Microscopical, > the Society, 



and Photographic Society " ) 



12 slides Mr. John Eogers. 



The thanks of the Club were unanimously voted to the donors. 



The following gentlemen were balloted for and unanimously elected members 

 of the Club :— Mr. W. H. Bennett, Mr. George J. Burch, Mr. Ernest Hinton, 

 Mr, W. H. P. Sheehy, Mr. Ernest Schloesser, Mr. Henry E. Symons, F.R.M.S., 

 Mr. Henry L. Sequeira, M.R.CS. 



Dr. John Matthews called the attention of the members to a contrivance of 

 his own, of which he had given some hint at the ordinary meeting of the club 

 in March last. On that occasion, it would be remembered that a paper was 

 read on behalf of Dr. Pigott, descriptive of a new instrument of his, which he 

 called the " cratometer," and which was designed to measure the linear magnify- 

 ing power of objectives ; and it would also be remembered that he (Dr. Matthews) 

 said at the same time that he had produced an instrument, the "calliper eye- 

 piece," by which he had been enabled to do this very simply and easily without any 

 reference to mathematical formulae. Accurate measurement was at the root of 

 all useful scientific research, and was especially important in observations with 

 the microscope, and it was most desirable that every observer should append to 

 drawings of objects the exact magnifying power employed. Their President, 

 Dr. Beale, had set them an excellent example in this respect, never giving a 

 figure of any object without specifying the number of diameters by which it was 

 magnified. It was, however, no easy matter to do this. The usual method was 

 to put the objective and object in their places, and compare the magnified 

 image, seen by one eye, with the scale marked on a foot-rule placed at the same 

 distance as the object, and seen at the same time with the other eye, so as to 

 arrive at an approximation to the actual proportionate enlargement. He had 

 himself thought it better to estimate both these measurements with one eye only, 

 and at the same time, and he had been enabled to do this very successfully by 

 the instrument now brought before their notice, and which was a modification 

 of his " calliper eye-piece." He had used first of all two of Quekett's indicators 

 together in the eye-piece, and then placed a stage micrometer instead of the 

 object, but he found that this was not made so as to enable one of the points to 

 be moved with sufiicient precision. He had, therefore, substituted for this 

 arrangement one of Jackson's eye-piece micrometers, removing the glass scale, 

 and had inserted the two points into the body of it. The points were each pro- 

 pelled by a screw of known value, and repelled by a spring. In this instance the 



