186 C. K. Wead—ILntensity of Sound. 
a sound wave. It is doubtful if the first and second can ever 
fork +59 C. in the most favorable case in table IV (Ut,, col. Bs 
Table LV is drawn up to show roughly the amount at our 
posal in these forks. Col. 2 is the same as col. 138, table 1, 3 
gives approximately the maximum value of z that can be given 
by a bow; 4, the corresponding ener, 5, the corresponding 
value of x obtained by extrapolation, since nee observations 
could not be made with such values of z; 6, the maximum rate 
at which energy is given up. Cols. 7-10 give similar data for 
an ordinary or average value of z Mayer* finds from the 
heating of a bit of rubber between the prongs of Ut, fork vi- 
brating electromagnetically, that 54 foot-grains of work are given 
up to the rubber in 10 seconds; this is equal to 10500 ergs. per 
sec. : the data in table IV would give this value of 2Vx when 
zis a little less than 9 div., or about 0°-4 mm.—a very satisfac- 
tory agreement. 
TABLE IV. 
1 oe | 3 4 5 6 i 8 9 10 
Fork.| 2V |Max. z Piex. avi « 2Ven | Av.2|Av.2V} « | Av. 2VK 
’ <isonsiaenaiaieatiiatiniaiiimiaiitts 
Ergs. Ergs, sec. Ergs. 
2? x 10? x 10* x 10? x 
Ut, 450) 30 405 27 110 ‘8 290 20 5800 
Ut; 1235! 20 | 490 226} 140 6 445 crt 4900 
Sol, 2250|. 13 380 45 70 5 560 22 12600. 
Ut, 3860 9 310 "32 100 4 620 22 13600 
Sol, 7500 7 370 "49 180 3 675 36 24000 
Ut, 12700 6 456 “61 280 3 510 36 18000 
The ultimate object for which these experiments were begun 
was to determine how much energy was needed to cause sensa- 
tion, or rather how much energy passed through 1 square cm. 
at the limit of hearing; for it was believed that the “ efficiency ” 
of the tuning fork would be higher than of other sources of a 
sound-wave. 
_ The forks were taken out of doors to a field where the listen- 
ers might be 300 feet distant from the fork. This was sounded 
on the frame described above, and the am litude observed when 
the different listeners shouted “out.” The separate observa- 
* This Journal, viii, 362. 
