CHAPTEK XXY. 



CLASSIFICATION OF OBJECTS HOW TO 

 TREAT THEM. 



While we can not attempt to give definite rules for the treat- 

 ment, microscopic or photographic, of every object or class of 

 objects that may come under the notice of the Photo-micro- 

 grapher, still in our somewhat varied experience of various 

 classes of objects we have noticed facts and formed opinions 

 which may be of service to our Readers. In hope, at least, 

 of such service being rendered we shall set down a few points 

 noted in our actual work. 



Insect preparations are almost always exceedingly difficult to 

 photograph well. In the first place if the insects are of any size 

 and are mounted in cells as they ought to be, and not flattened 

 by pressure as they sometimes are, we have to deal with the 

 optical " difficulty " of focusing at once various planes. To 

 meet this trouble the lowest available "power" should be 

 used, and stretch of camera substituted for eye-piecing as a 

 means of getting magnification, and even this does not 

 help us much. Making small negative images and enlarging 

 them will probably not help matters in the least, in our 

 experience " enlarging " has never been of any service in 

 overcoming the difficulty to which we allude. In our own 

 work the most marked successes in this line have been obtained 

 by the use of an apochromatic lens of YO millimetres, or 

 about 3 inches facal length, and a camera stretch of from 5 

 to Y-J feet. The illumination in a case such as this is apt to be 

 a puzzle, but the best plan is perhaps one suggested to the 

 writer by Mr. E. M. Nelson ; namely : to use as condenser the 

 field-glass of a good " A " eye-piece, placed close behind the 

 object, (i. e. between the object and the light), the convex sur- 

 face of the field-glass being turned towards the light. Other 



