44 PHOTO-MICROGRAPHS. 
The head of the fine-adjustment screw should 
be of as great a diameter as is practicable, and 
should be grooved around the margin for the pur- 
pose of carrying a cord, which will be required in 
focusing upon the screen. 
In working with a heliostat and with the high- 
est powers, a delicate centring apparatus for the 
achromatic condenser will be required, and all the 
movements of the stage and sub-stage with which 
first-class stands are provided will be desirable, 
if not absolutely necessary. The large stand of 
Powell & Lealand! is an excellent one for the 
purpose, and is that which is preferred by Wood- 
ward. 
Objectives. 
It is a delicate matter to recommend the objec- 
tives of certain makers, when there are so many 
competitors in the field; but in the interest of the 
purchasers of this little book, the Author proposes 
to give the results of his experience. No doubt a 
fair trial of the best work of makers not named 
would show that their objectives are equal to some 
of those for which a preference is expressed. 
Beginners are advised at the outset to make 
their first efforts with such objectives as they may 
possess, and to remember that the most expensive 
objectives are not necessarily the best for their 
purpose. Some of the wide-angled modern ob- 
jectives are practically useless for photography, 
1 See “The Microscope and its Revelations,” sixth edition, 
p. 90. 
