1887.] NEW-YORK MICROSCOPICAL SOCIETY. 69 



The two acknowledged leaders in photomicrographic literature 

 in the two great English-speaking countries, Drs. Maddox and 

 Woodward, throughout their writings have used the words in 

 question with the clearly defined Shadbolt distinction ; and the 

 writer trusts, with this historical note recorded in our Proceed- 

 ings, the American Society of Microscopists, as a body and as 

 individuals will insist upon the correct usage of these terms. 



A photomicrograph is a macroscopic photograph of a micro- 

 scopic object ; a microphotograph is a microscopic photograph 

 of a macroscopic object. 



Discussion. — In discussing this paper, Professor W. A. Rog- 

 ers took occasion to recommend the use of the term mikron in- 

 stead of micromillimeter, in which Professor W. H. Seaman con- 

 curred. — Proc. Am. Soc. Microscopists in Microscopical Bulletin 

 and Science News. — 



Tests for Definition, Penetration, &c. — The Microscopi- 

 cal Bulletin and Science News, Aug., 1887, takes the following 

 admirable extract from the English Mechanic, by E. M. Nelson. 



" This is an important subject, about which a great amount of 

 misconception exists. Let us first get at the meaning of the 

 words. According to Goring, Pritchard, and Brewster in 1837, 

 'Quekett,' second edition, 1852, 'Jabez Hogg,' second edition, 

 1855, penetration or 'separating power' = resolving power; 

 definition == freedom from spherical and chromatic aberra- 

 tions. So also Micrographic Dictionary, third edition, 1875, 

 with this exception, that according to it, separating power = 

 magnifying power. In 'Carpenter,' fifth edition, 1875, pen- 

 etration = focal depth ; so also in 'Beale,' fifth edition, 1880. 

 Probably the term 'penetration' came to mean resolution from 

 the phraseology used in connection with Herschel's monster 

 telescope 'penetrating' into space, and resolving very minute 

 stkrs, which were thought to be immensely farther off than the 

 more conspicuous ones. 



"The word 'penetration ' is now used solely with reference to 

 depth of focus. 



"The qualities of an object glass are six in number : 



1. Magnifying power. 



2. Resolving power. 



