532 



Prof. R. Threlfall and Mr. J. F. Adair. On the 



Discussion of Results. 



It will be convenient to collect here the main resnlts of the in- 

 vestigation as far as the comparison with the velocity of sonnd is 

 concerned. 



Table of Comparison. 



Class. 



Description 

 of explo- 

 sive. 



Number* 

 of experi- 

 ments 

 (complete). 



Temperature 

 at which 



comparison 

 is made. 



Velocity 

 found (pro- 

 bable). 



Velocity of 

 sound, cslcii- 

 lated. 



Excess of velocity 



found OV6T 



velocity of sound. 



A 



9 oz. of dry 

 guncot- 

 ton 



11 



17'79°C. 



met. per sec. 

 1732 ± 22 



met. per sec. 

 1523 



per cent. 

 13-75 





B 



10 oz. No- 

 bel's No.l 

 dynamite 



24 



14'5°C. 



1775 ± 27 



1508 



17-7 





C , 



18 oz. dry i 5 

 guncot- j 

 ton 



18-3° C. 



1942 ± 8 



1525 



27-3 





D 



64 oz. dry 

 guncot- 

 lon 





19° C. 



2013 ± 35 



1528 



31-7 



Though the regularity of the mean results is very satisfactory, a 

 glance at any of the Tables will show that several individual observa- 

 tions deviate to the extent of nearly f per cent. Now from our appara- 

 tus, and from the fact that the observations are to a great extent made 

 automatically, we are at a loss to account for these deviations, unless 

 they are real. We hope to be able to show the cause of this imme- 

 diately, for the moment we wish to add a little to what has already 

 been said as to the rejection of certain observations. When we first 

 began to get readings our gauges were not nearly so satisfactory as 

 they afterwards became ; the sensitiveness was sometimes so small 

 that we occasionally failed in obtaining any record whatever from the 

 apparatus which was furthest away from the firing point. The gauges 

 were also apt to allow water to leak in at the bottom, and the air 

 sometimes escaped slightly at the top, allowing the rubber faces to 

 collapse. Both these accidents tend to lessen the sensitiveness of the 

 gauges very materially. It was soon noticed that the abnormal 

 results — and these always occurred in the direction of making the 

 velocity too small — were obtained when the gauges were for some 

 reason or other more or less out of order. When, as shortly occurred, 

 we succeeded in making the gauges uniformly sensitive, and prevent- 

 ing water-logging and the escape of air, we got no abnormal times. 

 The only difficulty we experienced in deciding to reject certain obser- 



* Each experiment requires two separate explosions and time-measurements. 



