22 ON HIGH POWERS, AND A STEADY MICROSCOPE. 
Powell’s =.th that is not equally visible with a ;,th by 
Ross; further observation may, however, serve to elucidate 
points of evident advantage in the deeper power. It must 
be observed that the th does not work well with thicker 
covering glass than ‘0035, and in order to allow for some 
little distance of the object below the covering glass it is 
better to use 003. The ;th employed was originally cor- 
rected for covering glass of ordinary thickness, say ‘006 to 
‘007, and could not be adequately corrected by ‘separation of 
the anterior combination for glass only °003 inch thick. 
In order te compare the objective on the same object, it 
therefore became necessary to construct a new anterior com- 
bination for the -1,th, specially adapted to very thin covering 
glasses; and it now works as correctly with these as it does 
with the original combination, under the conditions which 
that was designed to fulfil.” 
Extract ITI. 
From the ‘ Intellectual Observer,’ page 51, August, 1864. 
“ My attention has recently been directed to some remarks 
contained in page 329 of your June number, alleging a dis- 
crepancy between a statement of mine, contained in my 
S Report on the Microscopes in the late International Exhibi- 
tion,’ that no objective yet manufactured for sale at all rivals 
in its power of development the th of Messrs. Powell and 
Lealand ; and another statement, contained in my ‘ Presiden- 
tial Address,’ delivered at the last annual meeting, that I 
have not hitherto succeeded in Bets a gs any point of 
organic structure with Powell’s ~,th that is not equally 
visible with a ~;th by Ross. This apparent contradiction 
has no real existence, Masmuch as the ~,th by Ross, to 
which I alluded (a great improvement on any previously 
made by him), was not in existence at the time to which the 
former observation refers; and in corroboration of my own 
opinion I may further state that, after having successively 
examined, together with Dr. Beale, with this ~,th and with 
his own =! th. (or !;th), several difficult preparations of tissue 
with which he was well acquainted, he remarked that he did 
not think he had ever seen some points of structure better 
shown than they were by my ;',th. 
“In the following page, 330, the writer asks, ‘When an 
object (other than diatom lines) has been seen with a 1th or 
th, can it not nearly always be shown by the jth 2 To 
