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



Departure from mean. 

 Vp = 210000 +8716 

 192568 -8716 

 201284 



Mean as above = 201284 



Hence probable error of mean (Peters) = 3474 



„ (Bessel) = 3394 



Thus the result of Class D may be written — 



Probable velocity at 19° C. = 2013 + 35 metres per second. 



The theoretical velocity of sound is 1528 metres per second. Tims 

 in each class the experimental velocity is greater than the theoretical 

 velocity of sound. 



During the experiments it sometimes occurred that the firing buoy 

 drifted slightly (by influence of wind and tide) from the line con- 

 taining the piles. The deviation from that line could only be 

 approximately estimated, but it was judged that it was never so 

 much as 3*5 metres, although it was usually slightly out of line. 

 S appose its distance from the line of the piles to be 35 metres, 

 and that the deviation at the other end was the same, then (see 

 figure) taking the distances as marked, A and B being the piles, 













r 















lii 



. - •■ ■ '■' '■' ■': . Li'"'"-. * /3 : 



. : ' — : — — — 











■ B ■ 



170 ■■■■■ 



••- A 



■' 2-3 





P the firing point, if the explosion occurs at time t, and if V be the 



velocity of transmission of the disturbance, this reaches A at time 



AP BP 

 t + -y- and reaches B at time t + and the first interval recorded 



on the smoked plate is 



BP-^-AP 



TT = — hTg+l^'i^ — ITj. 



The second interval of the shot from P' is 

 , AP'-BP' 



+ T 1 +ff il — T., — O-,. 



y 1 J i^°i 

 Hence, if BP-AP = AP'-BP' 



T + T _ BP-AP 

 2 ~ V 



