426 ‘ REVIEWS. 
is Mr. Bicknell, who says he saw them, and only with a Tolles’ 1-12. 
Hartnack does not say distinctly that he has seen them with a 1-16; he 
attempted to show them to two accomplished GRAN and both 
failed to see them. Dr. Eulenstein has also failed with Hartnack's Nos. 
10, 11 and 12, Powell and Lealand's 1-50 and Ross' brisa and Dr. 
Hagen knew these facts, for the writer told him before his paper was 
written; comment is unnecessary. Dr. Hagen also says that ne 
1-16 has resolved S. gemma, and Tolles’ 1-10 has not, ergo Hartnack’s has 
done what Tolles’ could not. Dr. Hagen has himself Agr the 
“direct proof" he wanted of the * cinese excellence" of the 
e 
Now for some of Dr. Hagen's errors and mistakes. He says of Tolles' 
objectives **the workmanship is superb,” “ the adjustment only moves the 
lower lens from the two others." The solid eye-pieces are ‘really bi- 
convex Coddington lenses.” He gives on the authority of Edwards a 
is not Tolles’ ce e eye-pieces are not Coddington lenses, and that 
Tolles had never made objectives to move the front lens; all of which 
Dr. Hagen could Sed easily ascertained. 
Dr. Hagen considers that **a most important fault of the instrument 
consists in the difficulty of its use. In order to adjust them so that they 
will give their greatest results requires delicate labor and considerable 
€ ek this Poem they are excelled — the denen as well as the lower 
of English and German." ‘Thee of treatment of Hartnack's 
iud. feriis senem aaa is Ere for less troublesome.” If this 
means anything it must refer to the delicacy of the adjustment for cov- 
ering glass. Undoubtedly sab en are far less troublesome. It is 
thought to be well known to microscopists that the delicacy of this ad- 
justment — consequently in one sense the difficulty of use — is increased 
a: "n proportion to the approach to perfection of the lenses. Certain it 
is that Hartnack when delivering an objective made for a member of the 
Boston Society of Natural History two years ago, called the purchaser's 
attention especially to the fact that when an object was best shown, 
the m 
astonished to see how much more the hand of the artist himself will 
develop with the instrument." 
The majority of the eat eae here are ‘ dilletanti or workers on 
diatoms ;” this must be news to Professors Holmes, Bacon, Ellis and T" 
and to their hundreds Mi past and present students; be “ truth will be 
