NATURAL PHILOSOPHY. 147 



out augmenting the cost of the instrument ; out of England, he is un- 

 doubtedly the best maker in Europe. To furnish an idea of what he 

 has done to diminish the cost of a good instrument, the following is a 

 comparison of the price of the objectives which were the subject of 

 the experiments : Ross, 306 francs ; Spencer, 230 do. ; Nachez, 60 ; 

 and, what is still more, he is constantly improving his lenses without 

 adding to their expense. The lower powers of the several makers 

 were examined without finding any sensible difference in the denning 

 effects of them ; what little there was, was in favor of Spencer. The 

 field of the three differed ; Xachez's being the least, and Spencer's the 



greatest. 



SPENCER'S AMERICAN MICROSCOPES. 



AT the meeting of the American Association, Albany, a committee, 

 consisting of Professors Bailey, of West Point, Torrey, of New York, 

 Smith, of Louisiana, Dr. Burnett, of Boston, and Clarke, of Albany, 

 were appointed to examine and report on the microscopes manufactured 

 by Mr. Spencer, of Xew York, a specimen of which was exhibited to 

 the Association. The committee subsequently presented the following 

 report : 



" The committee on microscopes have the honor to report that they 

 have carefully examined several sets of microscopic objectives, recently 

 manufactured by Mr. Charles A. Spencer, of Canastota, N. Y., and 

 that, after numerous trials with the most difficult test objects known, 

 they are unanimously of opinion that these lenses are of unrivalled 

 excellence. The perfection of these glasses was shown by their admi- 

 rable defining power, their unprecedented largeness of operation, but 

 preserving good working distance, and by freedom from defects of 

 lenses. The committee believe it unnecessary to report in detail the 

 different experiments made, but confine themselves to the statement 

 that, after numerous trials by all the modes and tests which have been 

 repeatedly employed by members of the committee in examining many 

 of the best foreign lenses, they arrived at results with Mr. Spencer's 

 objectives, which, they believe, have never hitherto been obtained by 

 any microscope in existence. The low powers, as well as the high 

 ones, excited their admiration, readily and beautifully resolving test 

 objects hitherto considered entirely beyond the reach of glasses of cor- 

 responding focal distance. As every improvement in the microscope 

 has a direct and most important influence on the progress of scientific 

 research, the committee believe they cannot express in too strong terms 

 their admiration of the results obtained by the unaided efforts of Mr. 

 Spencer, and, however reluctant to appear in a boastful attitude, they 

 bt-lieve it would be an act of injustice not to state their sincere convic- 

 tion, that Spencer's objectives are now the best in the world." 



NEW FORM OF MICROSCOPE, WITH IMPROVED METHODS OF MEASURING 

 THE DIMENSIONS OF OBJECTS AND THE ANGLES OF CRYSTALS. 



THE following is an abstract of a paper presented to the American 

 Association, Albany, by Dr. J. Lawrence Smith, on a new form of 

 microscope, and explained in connection with the instrument : 



