MICROSCOPY. 563 
mechanical means. Thus was reproduced the photograph of 
Amphipleura pellucida in the last April number of this Journal. 
In the Albertype process a printing surface (not a relief) is 
produced through the negative on a gelatine film by the action of 
light. The prints thus produced are, at present, less expensive 
_ than the Woodbury prints, and more convenient for book work, 
but the edition is less uniform. On enamelled paper the prints 
are handsomer, but will not bear much handling. 
Lenses Dry or Immersion. — Dr. Thomas Birt writes to the 
“Monthly Microscopical Journal” an enthusiastic notice of a 
“new” 1th by Ross, arranged to work wet or dry by screw collar 
adjustment and without change of front, a peculiarity shared only, 
as far as he (Dr. Birt) was informed, by Powell and Lealand’s jth. 
If the Ross tth is like some other recent lenses by the same house, 
it would be difficult to say too much for its excellence as an objec- 
tive: the one thing that could not be said of it is that it has any 
possible claim to priority in respect to the peculiarity mentioned. 
This expedient, like that of double fronts, is undoubtedly an 
American innovation. Objectives with double fronts and with 
double backs were made by Tolles and by Wales years ago, and 
Were taken to -London and exhibited there in advance of any 
knowledge of such a contrivance there. Lenses to work either 
wet or dry, by cover adjustment. only, have been so generally 
made and familiarly used in this country as to be not now looked 
upon as an innovation at all. The question of priority is possibly 
a difficult one, but both Wales and Tolles made and sold them 
freely, long before any claim to any such arrangement was made 
* by any foreign maker. Wales, as early as August 1867, made 
two objectives of this kind, to work both wet and dry with the 
Same front, and they were exhibited at the Fair of the American 
Institute in New York, and received a first premium medal and 
diploma bearing date of October 1867; he was advised to patent 
; improvement at the time, but did better than that, and cer- 
tainly ought to be favorably remembered for having given it to us 
for nothing. Tolles also constructed these objectives about the 
_ Same time, having made such an objective and delivered it to a 
T as early as-June 29th, 1868, and the objective of the 
above date is still in existence, and is considered one of the best 
that have yet been constructed on that plan by its maker. 
