THE JOURNAL

OF THE-

FRANKLIN INSTITUTE,

DEVOTED TO

SCIENCE AND THE MECHANIC ARTS.

EDITED BY

Prof. Persifor Frazer, D.Sc., Prof. Edwin J. Houston, Theo. D. Rand,
Prof. Coleman Sellers, Prof. H. W. Spangler, Committee on Publications,
with the Assistance of

Dr. Wm. H. Wahl, Secretary of the Institute.

VOL. CXXXII.-Nos. 787-792.

JULY TO DECEMBER, 1891.

PHILADELPHIA:

Published by the Institute, at the Hall, 15 South Seventh Street.

1891.