THE

JOURNAL

OF THE

FRANKLIN INSTITUTE

DEVOTED TO

SCIENCE AND THE MECHANIC ARTS,

PUBLISHED BY

THE INSTITUTE,

Under the Direction of the Committee on Publication.

Vol. CXII.-Nos. 667–672.

THIRD SERIES.

VOL. LXXXII.-JULY TO DECEMBER, 1881.

PHILADELPHIA:

FRANKLIN INSTITUTE, NO. 15 SOUTH SEVENTH STREET.

1881.