J. M. Ordway on Waterglass. : 337 
Also, by altering the focus, an apparent reversal of the lights 
and shades takes place, the positions of the bright circular dots 
being seemingly occupied by dark dots; this is caused by the 
expansion of the thicker portions of the dark spaces between the 
circles, and so far as I can judge, with the means at my command, 
the reversal of the lights and shades in the dots on this test ob- 
ject examined by the microscope, under the imperfect focal adjust- 
ment, is due to the same cause, and is more apparent than real. 
_ As it is impracticable to publish prints from these negatives 
in this Journal, samples will be sent, on application by letter, to 
those who may be particularly interested in this subject. 
Troy, September 7th, 1861. 
Arr, XXXVIIL— Waterglass ; by J. M. ORDWAY. 
(Continued from page 165.) 
Parr II. : 
ee it dissolves without much difficulty in water kept aad 
at 
bits retain to the last their exact original form, 
hee rted a certain sample of pure 
silicate of soda to be insoluble. Yet T found that forty-five 
minutes boiling of the same silicate, in the same state of division, 
the Coarsely ground silicate in the ke 
AM. Jour. Sc1.—Szcoxp Serres, VoL. XXXII, No. 96,—Nov., 1861. 
43 
