of the Relative Intensities in Sound. 125 - 
preening results worthy of the appellation of measures of 
precis 
2. D icceneas of the of various substances to transmit 
and to reflect sonorous vibration 
After we have succeeded in oben a measure of the inten- 
sity of the vibrations of the air at a certain distance from the 
sounding body, we can measure the poewrs of various sub- 
stances to transmit, absorb and reflect sonorous vibrations. 
To accomplish this I place one of the sounding bodies in the 
ocus of a parabolic reflector and bring the two resonators at 
such distances from their sounding bodies that the intensities 
of the pulses traversing their respective tubes are equal. We 
then place in front of, but not too near, the mouth of the reson- 
ater, in front of the reflector, the plane surface of the substance 
. In the Smithsonian Report for 1857 will be found an account of very inter- 
esting vege valuable experiments, by Prof. Joseph Henry, bearing on “ Acoustics 
* age to Public Buildings.” I by thee’ — Pr of. Henry determined 
é powers i 
i 0 
during 252 seconds. Placed on a large, thin pine board, its vibrations lasted about 
10 seconds. In this ease “the shortn riness of duration was com mpensated fo for by the 
ced.” 
greater in 
+ marble slab, a solid brick wall, and on a wall of lath _ ‘plaster, its vibrations 
pa ively 115 seconds, 88 seconds, and 18 second 
Place a cube of india dren the igre serena : the fork was scarcely 
cn hey whet it was susy om the ric ore he but its - rong 
Y 40 seconds. H hi aliéi what became of the impulses 
ere Henry puts y e que oa: Peleus 
the tuning-fork? They were neither transmitted throu ugh 
nor given off to the air in the form of sounds; but were probably expended in 
Producing a change in the matter of the india-rubber, or were conve into 
0! y= Thi iv ‘ nee witht this 
heat, or both. Tho e of 
gh the inquiry did not fall 
Series of investigations, yet it wan at interesting point 
of view to dete ine | hether ~. was actually produced, that the following ex- 
periment was mad * The point of a compound wire fo copper and 
andy aco rust into he aha tance of a — = _ = ends of the wire 
wi licate galvanometer. The 
ns st, th ing-fork was A i brated, and i : Bae ses : rane to the 
rubber, A very perceptible increase of perature was th The needle 
moved throug re of ne to two and a degrees. The riment 
Was varied, and many times repeated ; the motions of the needle were always in 
t . . . : the 
he same direction, namely, in that which was produced cue wee 
so i and although several e: - 
ters have cdipenon obtained tie eae oo not one of them gives He: 
“hae antecedent work. In 1868 I published a full account of the above ex- 
nt in my Lectur: 79. Va a. 
In the same paper rides Bceee ri a few qualitative tions ae 
Powers of various substances, by placing a watch ge ra ana 
and focus of a a mirror; he then receded along the axis of the ve 
Sonorous beam, wi hearing trum Paper flannel 
and were no 
pateen the wath id the miro, snd the scorn F of the sound ‘ak found to 
diminished by the retiecting and absorbing powers of ubstances. 
