ADTANCEMENT OF SCIENCE. 137 



it was of so interesting a character, in a physical point of view, to determine 

 ■whether heat was actually produced, that the following experiment was made: — 



A cylindrical piece of India rubber, about 1| inches diameter, was placed in a 

 tubulated bottle -with two openings, one near the bottom and ihe oLber at the top; 

 a stuffing box was attached to the upper, through which a metallic stem, with a 

 circular foot to press upon the India rubber, was made to pass, air tight. The lower 

 tubular was closed with a cork, in the perforation of which a nh'e glass tube was 

 cemented ; a small quantity of red ink was placed m the hole to serve as an index- 

 The whole arrangement thus formed akiud of thermometer, -which would iudicate 

 a certain amount of change of temperature in the inclosed air. On the top of the 

 stem the tuning fork was screwed, and consequently its vibrations were transmitted 

 to the rubber within the bottles. The glass was surrounded with sevcal coatings 

 of flannel to pi event the influence of the external temperature. The tuning fork was 

 then sounded, and the vibrations w ere kept up for some time. No reliable indica- 

 tions of an increase of temperature were observed. A more delicate method of 

 making the experiment next suggested itself. The tube containing the drop of red 

 ink, with its cork, was removed, and the point of a compound wire formed of cop- 

 per and iron was thrust into the substance of the rubber, whilst the other ends of 

 the wire were connected with a delicate galvanometer. The needle was suffered 

 to come to rest. The tuning fork was then vibrated, and its impulses transmitted 

 to the rubber. A very perceptible increase of temperature was the result. The 

 needle moved through an arc from one to two and a half degrees. The experiment 

 was varied, and many times repeated ; the motions of the needle were always in 

 the same direction, viz : in that which was produced when the pointof the compouud 

 wire was heated by momentary contact with the fingers. The amount of heat gen- 

 erated in this way is, however, small, and, indeed in all cases in which it is genera- 

 ted by mechanical means, the amount evolved appears very small in comparison 

 with the labor expended in producing it. Jule has shown that the mechanical en- 

 ergy generated in a pound weight, by falling through a space of 750 feet, elevates 

 the temperature of a pound of water one degree. 



It is evident that an object like India rubber actually destroys a portion of the 

 souud, and hence in cases in which entire non-conduction is required, this substance 

 can probably be employed with perfect success. 



The tuning fork was next pressed upon a solid brick wall. The duration of 

 vibration, from a number of trials, was eighty-eight seconds. Against a wall of 

 lath and plaster the sound was louder, and continued only eighteen seconds. 



From these experiments we may infer that if a room were lined with a wainscot 

 of thin boards, and a space left between the wall and the wood, the loudness of 

 the echo of a single noise would be increased, while the duration of the echo would 

 be diminished. If, however, the thin board were glued or cemented in solid con- 

 nection to the wall, or embedded in the mortar, then the effect would be a feeble echo, 

 and a long continued resonance similar to that from the slab of mable. This was 

 proved by first determining the length of continuance of the vibrations of a tuning 

 fork on a thin board, which was cemented to a flat piece of marble. 



A' series of experiments were next commenced with reference to the actual 

 reflection of sound. For this purpose a parabolic mirror was employed, and the 

 sound from a watch received on the mouth of a hearing trumpet, furnished with 

 a tube for each ear. The focus was near the apex of the parabola, and when the 

 watch was suspended at this point, it was six inches within the plane of the outer 



