C. K. Wead—Intensity of Sound. 185 
Even when the conditions were similar, so far as known, 
considerable differences were found in x for the same values of 
z', 2’, as table III shows for two forks; the last line has been- 
used in the succeeding computations when the table shows 
more than one set of observations. I suspect that a part of the 
variability of 6 may be due to a different strength of the over- 
tones at different times. 
The numbers in column 8, table III (taking the last line for 
Sol, and Ut,), show such a regular increase as to render it at 
least plausible that the term containing 4 depends on the resist- 
ance of the air to the faces of the prongs. Schellbach* has 
shown that the resistance of the air to discs varies as v®, even 
when v is as low as 17-1cm. per sec. In these forks the mean 
velocity will be = x on = 0181827 em. per sec., where z is 
given in micrometer divisions, and x is the vibration-frequency. 
If the forks have the amplitudes given in table f column 7, 
of the fork when other conditions remain the same: ; 
- R=(-01818)2z2n2/-x a constant; by Mercadier’s formula 
(6) n/?= a constant. | ‘ 
(22) .°. R=kz2n!, where & is a constant depending on the 
breadth, thickness and modulus of elasticity of the prongs, the 
form of the curve which the vibrating prong assumes, the den- 
sity and viscosity of the air, and perhaps on other things; but — 
for the forks of this series it is considered constant. Accord- 
ingly 6 in table III, col. 8, should vary as n°. 
i . 
aking Ut,=1 we get the two series: 
nt = 1: 2°83 5-2 8° 14°7 226° 
6 = 003 008 028 022 044 062 
10005+n? = 3 a8 5-4 27 3° 7 
Considering the difficulty of determining } with accuracy, the 
close agreement of the quotients in the last line seems remarka- 
le. No change has been made in table III since these caleu-— 
lations were made; so there has been no possibility of biasing 
the judgment in favor of this regular increase of b. 
The energy that the fork loses is expended in these ways: 
1. In heating the fork, and the wood of the resonance case; 
2. In communicating tremors to the support; 8. In producing = 
* Pogg. Ann., exliii, 10. 
