Geology and Naturai History. 217 
Royal Society, June 20, 1872. The account is republished in the 
Phil. Mag. for Nov., 1872. The ruled plates were laid upon glass 
plates sensitized in the usual manner, and the prints were made in 
the same manner as from ordinary negatives. Both wet and dry 
Sensitive plates were used, with but little difference in the results. 
r 
very conveniently in an ordinary spectroscope, by putting them in 
the place of the prism. Gratings having 6000 lines to th aren 
successfully made, and as their cost is trifling compared with that 
of the ruled ones, they will be much more accessible to experimen- 
of rock-salt, 
Il. Grotogy anp Natura History. 
h g the 
_ 8mount at 24 inches, and the loss from the movement of the glacier 
two to two and a half inches, there would have yuired | ; 
further loss of about nine-tenths of the whole by evaporation — 
melting to have kept the top of the glacier ata nearly uniform — 
The amount of loss from evapo and melting was undoubt- 
edly far greater than has been estimated on page 207; for that 
from evaporation is large even in the Arctic; and both <a 
of waste may in some years have carried off all the snows that 
