182 C. K. Wead—Intensity of Sound. 
watch was used (an “ Auburndale timer”), held in the left. 
hand, while the right hand was free to use the bow and make 
records; the pointers gave directly ¢ second. Thus the time 
was found which’ was necessary for the amplitude to decrease 
from 2’ to 2’. An example will indicate in a general way the 
accuracy of the method. Fork Ut,; 2’=12 div., 2’=6 div.; 
_ time = 98, 93, 10, 11, 104, 93, 98, 104, 10, 94, 104, 103; mean 
10:08 sec. These were not consecutive observations, and sev- 
paratively broad to be seen; while if z is small the finite 
breadth of the “point” and of the lines on the scale leads to 
uncertainty. 
able II gives for one of the forks used the mean value of x 
for a number of intervals. Itis an unexpected fact that x varies 
so much with the amplitude; only Poske,* so far as I have dis- 
covered, refers to it, and then incidentally. It is a proof that the 
resistance to the motion of a fork is not expressed by a term 
proportional to the first power of velocity simply, but the second 
and perhaps higher powers must come in; the equation of 
motion would be ti+zxi+2u?+-n2u=0. But this is not inte- 
grable, and even the results which Poisson gives for the case 
when z=0 shed no light on this case; we must therefore deter- 
mine x empirically as a function of z and introduce the corres~ 
ponding value of x into equation (14), 
TABLE II. 
1 2 ee ne 6 7 8 9 
| | 
+2" 
Fork. |No. obs.| 2’ | 2” | s t |K obs. | x comp. | Dif 
: | s) : 
| 
Sol, 6 | 10] 5 | 75 | 4:70} -295 | -295 | +000 
4 9| 3] 6 05| °243 acs + 16 
2 9| 2) 5b | 1430} -210 3931 52S 
2 8| 5| 66} 319] 293 267 |+ 26 
1 | oh 446 + bal 268 | 203 14+ 8 
4 | 81°31] BO} S19);--aR9 | ~-3B9 0 
4 8| 2) 6 | 1981] 216 | ‘225 |— 9 
4 iG Se ci ae ae Sy 900 oI 8 
2 ¢fo92 @ 1320 | 900 | 18T 1+ 8 
6 eae hee nat loo |. er be 8 
5 5} 2 3B | 10°05) °182 jas [m4 
$16) 81% 17| *170 160 [a 2 
3 4| 1| 25| 1775] 156] 155 |+ 1 
55 + 48 
13)” 49 
+°008 
It will be seen that the observations are fairly represented: oe, 
__ by putting 
i *Pogg. Ann., clii, 470. 
