168 



THE AMEKICAN MONTHLY 



[September, 



March, 1S54. Mr. Tolles combined 

 many qualities essential to the great 

 work of his life, the improvement of 

 the microscope. To great theoretical 

 and practical knowledge of the sci- 

 ence of optics he united mechanical 

 and inventive genius and marvellous 

 skill of eye and hand. While still in 

 the service of Mr. Spencer he devised 

 the form of cover-correction for ob- 

 jectives in which back and middle 

 combinations have a rectilinear mo- 

 tion only, and the front remains en- 

 tirely stationary. In 1853 he invented 

 and patented his solid eye-piece. In 

 1858 he made his first immersion ob- 

 jectives, though, of course, this plan 

 was not original with him. In 1858 

 he consti^ucted objectives with two 

 fronts, one to be as an immersion and 

 the other dry. In August, 1873, he 

 made the great step forward which 

 placed him at the head of his profes- 

 sion, the Columbus of a new era of 

 microscopy. He made an immer- 

 sion one-tenth with an aperture 

 greater than that corresponding to 

 infinitely near 180 degrees in air. It 

 was a three-system lens, and had an 

 aperture of more than no degrees in 

 balsam, or 1.27 n. a. The same 

 month he made his first lens of the 

 duplex front formula a one-fifth, gly- 

 cerin immersion of no degrees bal- 

 sam angle. Both passed into the 

 possession of the Army Medical Mu- 

 seum at Washington, and both were 

 practically homogeneous immersion 

 lenses, as they gave the very best re- 

 sults when immersed in soft balsam, 

 which had been brought as nearly as 

 possible to the same index of refrac- 

 tion as the crown-glass of which their 

 front lenses were made, viz., 1.525. 

 The importance of this bold step and 

 its influence upon the progress of mi- 

 croscopy can scarcely be estimated at 

 this time, but it is certain that it was 

 the cause of a revolution of opinion 

 and practice among users and makers 

 of microscopes all over the world. 



'Mr. Tolles was the iuA^entor of 

 many other devices and appliances 

 for the microscope. In 1866 he in- 



vented and patented his stereoscopic 

 binocular eye-piece; in 1878 he re- 

 ceived two patents for improvements 

 in the microscope stand. For years 

 his stands were models of elegance, 

 convenience, and stability, and his 

 mechanical stages are, I believe, un- 

 equalled to-day for delicacy of con- 

 struction and perfection of working. 



' During his last illness, when he 

 could no longer go to his shop, he 

 had his microscope brought to the 

 hospital, and there on his death-bed 

 examined and tested his lenses till the 

 physician took it from him and for- 

 bade his using it longer. The amount 

 of suffering he endured can hardly be 

 estimated, but the fact is that many a 

 night during the last two years of hi« 

 life he could only get a broken sleep 

 while sitting up in his chair, the con- 

 dition of his lungs making it impos- 

 sible for him to lie down.' 



Professor Kellicott read an abstract 

 of a paper entitled ' Observation on 

 Infusoria, with Descriptions of New 

 Species.' Dr. Frank L. James read 

 a paper on the ' Deposition of Silver 

 on Glass.' 



A committee consisting of Pro- 

 fessor Rogers, Dr. Blackham, and 

 Dr. Detmers was appointed to report 

 a plan for securing funds with which 

 to erect suitable monuments to the 

 memory of Robert Tolles and Charles 

 A. Spencer. 



At the afternoon session Ernst" 

 Gundlach read the following paper 

 on ' Improvement in Objectives :' — 



' Eight years ago I presented to the 

 American Association for the Ad- 

 vancement of Science a description 

 of a new quadruple objective for as- 

 tronomical telescopes. The general 

 acknowledgment with which the pa- 

 per was received, and the high esti- 

 mation of the theoretical principles 

 of the invention, by scientific authori- 

 ties of this country as well as Europe, 

 encourage me to present to this Asso- 

 ciation a description of another im- 

 provement in objectives, which I ex- 

 pect will be of equal value to both 

 the telescope and the microscope. 



