206 
ME. EOBEET MALLET ON VOLCANIC ENEEGrY. 
that they throw some additional light upon the conjectured thicknesses that have been 
assigned to the earth’s solid crust, as well as upon the question left undecided by 
Laplace as to how far the effects of contraction due to refrigeration would be astrono- 
mically observable during the period of scientific history. In the author’s paper above 
referred to he has only dealt with the total contraction of the slag experimented upon 
between the temperature of its issue from the blast-furnace (viz. 3680°) and that of the 
atmosphere (53°), or by volume from 1000 to 933 for 3617° Fahr., from which the 
Eev. O. Fisher has calculated a mean coefficient of contraction =0-0000217 for 1° Fahr. 
(Geol. Mag., February 1874). This, though sufficient for that able writer’s immediate 
object, is not quite correct, as it treats the curve of contraction (Plate x. Philosophical 
Transactions, 1873) as a straight line. And in order to make use for our present 
purpose of these experimental contractions, it is necessary to obtain partial mean coeffi- 
cients for different portions of the entire curve. This the author has done for ranges 
of about 500° between the temperatures of the blast-furnace and that of the atmosphere. 
The diagram fig. 1 (reduced from Plate x. Philosophical Transactions, 1873) shows the 
Pig. 1. — Curve of Total Contraction of Slags. 
Volume. 
1014 
Coefficient. 
00001061 
1000 
0-0000477 
9877 
00000257 
976-9 
0-0000186 
967-6 
0-0000167 
959-35 
0-0000147 
0-0000144 
944-8 
0-0000136 
938 
933 
0-0000100 
Temperature. 
