ANDREW GRAY

LL.D., F.R.S., V.-P.R.S.E.
PROFESSOR OF NATURAL PHILOSOPHY IN THE
UNIVERSITY OF GLASGOW

PUBLISHED IN LONDON BY
J. M. DENT & CO., AND IN NEW
YORK BY E. P. DUTTON & CO.

1908
Richard Clay & Sons, Limited,
BREAD STREET HILL, E.C., AND
BUNGAY, SUFFOLK.