238 0-H. L. Smith on a new Illuminator for Opaque objects. 
Art. XXIV.— On a new Illuminator for Opaque objects under high 
powers of the Microscope; by H. L. Smiru, of Kenyon College. 
In attempting to study the structure of the diatomaceous frus- 
tule, I found it impossible to view it with high powers as an 
Opaque object, by any means hitherto devised. In a valuable 
paper on the scales of the Podura, (Mic. Jour., N.S. vol. ii, p. 
86), Mr. Richard Beck has stated that there is no difficulty in 
viewing them as an opaque object with the 4th in. objective and 
condensers rightly placed. Any illumination of Diatoms thus 
obtained is almost useless, from the great obliquity of the light, 
and with powers higher than the 4th in. is quite impossible. 
Mr. Ross's ingenious arrangement, suggested by Mr. Brooke, 
of a plain reflector, flush with the front surface of the objective, 
screw” at the top, to attach it to any — 
. bottom, to receive any objective; 
—and.so constructed that it can be placed in any position with re- 
to the light. A brass 2 rew and mil 
brass draw, moved by screw and led 
