354 



the latter with the former line determined, whence the direct distance 

 between the mean centre of each particular " heading," or mine, 

 and the observer's station, was trigonometrically deduced. 



The following table gives part of the results obtained from six 

 good experiments. 



TABLE. 



One very remarkable result is at once apparent on inspecting this 

 table viz. that the transit rate tends to increase in velocity with the 

 increased quantity of powder fired ; in other words, that the loss of 

 velocity in the same rock is less in some proportion as the force of 

 the originating impulse is greater, and so its amplitude greater at 

 starting. This is seen if the experiments be arranged in the order 

 of increased weight of powder. 



Experiment No. 1 forms the only apparent exception, and even 

 there the departure is not large. 



This fact, now for the first time (so far as the author knows) ex- 

 perimentally proved, appears remarkably in coincidence with the 

 theoretical researches of Mr. Earnshaw. 



The general mean transit velocity derivable from all the experi- 

 ments taken together gives 1176'407 feet per second for the rate. 

 The results, however, obviously form two groups viz. Nos. 1, 2, 3 

 and 6 from the smaller, and Nos. 4 and 5 from the greater charges 

 of powder. The mean from the first four is 1088'5597 feet per 

 second; that from the two last 1352 4 101 5 feet per second; and 



