/ 
678 ]ME. MALLET ON THE TEANSIT-VELOCITY OF EAETHQI7AEH WAYES. 
and as H=5 feet, V=17’935 feet per second, we have 
K^=Yy:^=0-576 for the slate, 
and 
E5=^^7^||=0'558 for the quartz, 
numbers which differ so slightly from equality, as to indicate that there is uo great dif- 
ference of transmissive power in the two rocks. Indeed this is rendered certain by con- 
sideration of the experiments themselves. Previously to their commencement I expected 
that in every instance the range in quartz would have been extremely short in relation 
to that in slate, and very nearly the same in all cases. The circumstances of the works 
subsequently obliged me to increase the range in the quartz, and to adopt “ headings ” 
for experiment, three of which have a range in quartz of nearly double that of the other 
three, as seen in the two following Tables. 
Table IV. — Shortest Eanges in Quartz. 
No. of experiment. 
Uncorrected transit- 
rate. 
Eange of quartz. 
Eange of slate. 
2 
5 
6 
Uncorrected mean 
Ratio of ranges in 
feet per second. 
967*93 
1210-79 
996-11 
transit-rate of Nos. 
quartz to slate 
feet. 
1600 
1300 
1400 
2, 5, 6 1058* 
... 1:2-66. 
feet. 
3877 
3738 
3829 
27 feet per second. 
Table V. — Longest Eanges in Quartz. 
No. of experiment. 
Uncorrected transit- 
rate. 
Eange of quartz. 
Eange of slate. 
1 
4 
3 
Uncorrected trans 
Ratio of ranges in 
feet per second. 
896-12 
1173-87 
977*26 
t-rate, mean of Nos 
quartz to slate 
feet. 
2850 
2700 
2650 
1,4, 3 1015 
... 1 : 1*32. 
feet. 
3733 
3704 
3727 
'75/eet per second. 
In each of the two groups everything is as nearly as possible alike ; there are two 
explosions of moderate charges, and one great explosion in each; they differ only in 
this, that in the first group, (Table lY.) the range in quartz, in proportion to that in 
slate, is very nearly double that in the latter (Table V.), being in the ratio of 2-66 : 1-32 ; 
yet, as will be observed, the mean transit-rate in both groups is almost alike, being in 
the ratio of I058’27 : 1015'75. This would be obviously impossible, if either one rock 
or the other exercised any well-marked accelerating or retarding influence upon the 
transmission of the w'ave. 
I hope shortly to be able to lay before the Society the results of some experiments 
upon the modulus of elasticity of perfectly solid portions of both these rocks, with 
