222 



REPORT — 1861. 



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 experi- 

 ment, 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 Ranges in Quartz. 



No. of experiment. 



2 

 5 

 6 



Uncorrected 

 transit-rate. 



feet per sec. 



967-93 



1210-79 



996-11 



Range of quartz. 



Uncorrected mean transit-rate of Nos. 2, 5, 6 



Ratio of ranges in quartz to slate 1 : 2-66. 



Range of slate. 



feet. feet. 



1600 3877 



1300 3738 



1400 3829 



,.1058-27 feet per second. 



Table V. — Longest Ranges in Quartz. 



No. of experiment. 



1 



4 

 3 



Uncorrected 

 transit-rate. 



feet per sec. 

 896-12 

 1173-87 

 977-26 



Range of quartz. 



Uncorrected mean transit-rate of Nos. 1, 4, 3 



Ratio of ranges in quartz to slate 1 : 1-32. 



Range of slate. 



feet. feet. 



2850 3733 



2700 3704 



2650 3727 



1015-75 feet 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 IV.) 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 

 1058-27 : 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 wave. 



In their direct relation to seismology the interest of the foregoing results 

 is not as great as when some years since I commenced these experiments. 

 At that period no knowledge whatever existed as to the relation that subsists 

 in nature between the velocity of transit and the velocity of the particles in 

 wave-movement in actual earthquakes. Geological observers, in fact, did 

 not appear to be aware of any such physical distinction ; and those who were 

 so, presumed that the velocity of the particles M^as like that of transit, ex- 

 tremely great, and that some simple relation would probably be found 

 between them. 



The first determinations of velocity of the particles in wave-movement that 

 have ever been made, namely, those by myself of the great Neapolitan earth- 

 quake of 1857, have dissipated this notion, however, and proved that the 

 velocity of the particles in even the greatest shocks is extremely small, not 

 exceeding 20 feet per second in very great earthquakes, and probably never 

 having reached SO feet per second in any shock that has occurred in history. 



