Scientific Lectures. 43 



The lecturer then proceeded to exhibit and explain different forms 

 of the misroscope, the ordinary compound microscope, the binocular 

 microscope, the inverted microscope, used for chemical purposes, the 

 double, triple, and multiple microscope, the solar, or calcium light 

 microscope, &c. ; after which he spoke of the modes of illumination, 

 and described a number of forms of accessory apparatus, together 

 ■with the modes of measuring the dimensions of microscopic objects, 

 and of determining magnifying powers. He referred also to the 

 wonderful perfection of mechanical art iu recent times, as illustrated 

 in microscopic ruling and engraving, and mentioned Robert's test- 

 plates, of which the finest lines, 120,000 to the Paris inch, have never 

 been, as yet fairly resolved, Drs. Curtis and Woodward, of Washing- 

 ton, have made enlarged photographs of these lines, as high as 96,000 

 to the Paris inch, or more than 90,000 to the English inch. He spoke 

 also of an engraving executed for him last year, by Dumoulin Fro- 

 ment, of Paris, representing the seal of Columbia College, with all 

 its pictorial devices, and its mottoes in Latin, Greek and Hebrew, 

 all clearly legible under the microscope; but the whole executed 

 "within a space less than one millimetre in diameter, or about the 

 size of the puncture of a pin in a sheet of paper. 



Speaking of the constructors of microscopes, he mentioned a nimi- 

 ber of American opticians, whose work is unsurpassed by that of the 

 most accomplished foreign artizans. Among the names mentioned 

 ■were those of Tolles, of Boston, and Wales of Xew York, both of 

 whom received silver medals at the Paris Exposition of 1867, and 

 also Granow, of J^ew York, and Zentmayer, of Philadelphia. He 

 Bpoke particularly of the " wet-front," or " immersion " objectives 

 of Wales and Tolles, as surpassing anything of similar power yet 

 constructed abroad. Some time was then devoted to the exhibition 

 of various objects illustrative of the power of the microscope, and of 

 the curiosities of natural history ; among which were some beautiful 

 enlarged photographs of diatoms^ animal muscle, (fee, prepared by 

 Drs. Curtis and WoodAvard, at the Army Medical Museum, at Wash- 

 ington, and lent for this occasion by the courtesy of the Surgeon- 

 General. [This part of the lecture hardly admits of a report.] 



The lecturer concluded as follows : I have thus presented you, as 

 well as my ability and the limited time allotted to me would allow, 

 a description of what, perhaps, may be justly regarded as the most 

 elegant of the instruments which modern science has created to aid 

 its investigations, and I have placed before you some examples illus- 



