46 PHOTO-MICROGRAPHS. 
inch, and one-half-inch (with cover correction) of 
Powell & Lealand, of London; the two-inch and 
four-tenths-inch of Tolles (Boston) ; the one-inch 
and one-fourth-inch of Collins (London) ; the two- 
thirds-inch and one-fifth-inch of Beck (London) ; 
the one-sixth-inch of Spencer (Geneva, N. Y.); 
the one-sixth-inch (DD), dry, and the one-eighth, 
one-twelfth, and one-eighteenth inch homogeneous 
immersion objectives of Zeiss (Jena, Germany). 
This list could no doubt be greatly extended, but 
the writer has refrained from recommending any 
objectives except such as he has himself practically 
tested in photography. 
The homogeneous immersion objectives possess 
decided advantages, and the one-eighteenth of 
Zeiss is to be especially commended to those who 
require so high a power. It is doubtful whether, 
in the present state of optical science and art, it 
is worth while to look for anything superior to 
this. That other makers may equal it, is quite 
probable, and immersion objectives which have the 
high guaranty of coming from such makers as 
Powell & Lealand, of London, or Tolles, of Boston, 
may be purchased without hesitation. I have re- 
cently seen an immersion one-eighth by Gundlach, 
of Rochester, N. Y., with which I was much 
pleased. The great objection to the best American 
objectives is their cost. The water-immersion ob- 
jectives of Hartnack are excellent, and are more 
conveniently used, especially for extemporaneous 
preparations, than are the homogeneous immer- 
sion lenses. 
