in Ruling his Test-Plates. By William A. Rogers. 91 
formed by dissolving white wax in gasolene, and uniting the solu- 
tion by emulsion with liquid gelatine. The coating thus formed 
will receive lines as fine as 10,000 to the inch, while its protecting 
qualities are sufficient to withstand very strong fumes. The sub- 
sequent experiments detailed in this paper have occupied my atten- 
tion from time to time during the past three years, when not 
engaged in my regular duties as Assistant in the Observatory.— 
Proceedings of the American Academy of Arts and Sciences. 
VOL. XVI. 
H 
