136 AMERICAN ASSOCIATION TOR THE 



and of the two prongs give a sonorous vibration to the air, which, if received upon 

 another tuning fork of precisely the same size and form, would reproduce the 

 same vibrations. 



It is a fact well established by observation, that when two bodies are in perfect 

 unison, and separated from each other by a space filled with air, the vibrations of 

 the one will be transmitted to the other. From this consideration it, is probable 

 that very nearly the same effect ought to be produced in transmitting immediately 

 the vibration of a tuning fork to a reflecting body as to duration and intensity, as 

 in the case of transmission through air. This conclusion is strengthened by float- 

 ing a flat piece of wood in a vessel of water standing upon a sounding board ; 

 placing a tuniug fork on this, the vibrations will be transmitted to the board 

 through the water, and sounds will be produced of the same character as those 

 emitted when the tuning fork is placed directly on the board. A tuning fork was 

 suspended from a fine cambric thread, vibrated in air, and, from the mean of a 

 number of experiments, was found to continue in motion 252 seconds. In this ex- 

 periment, had the tuning fork been in a perfect vacuum, suspended without the 

 use of a string, and further, had there been no etherial medium, the agitation 

 of which would give rise to light, heat, electricity, or some other form of etherial 

 motion, the fork would continue its vibration forever. 



The fork was next placed upon a large thin pine board — the top of a table. A 

 loud souid, in this case, was produced, which continued less than ten seconds. The 

 whole table, as a system, was thrown into motion, and the sound produced was as 

 loud on the under side as on the upper side. Had the tuning fork been placed 

 upon a partition of this material, a loud sound would have been heard in the ad- 

 joining room ; this was proved by sounding the tuning fork against a door leading 

 into a closed closet. The sound within was apparently as loud as that without 



The rapid decay of sound in this case was produced by the great amount of the 

 motive power of the fork being communicated to a large mass of wood. The in- 

 creased sound was clue to the increased surface. In other words, the shortness of 

 duration was compensated for by the greater intensity of effect produced. 



The tuning fork was next placed upon a circular slab of marble, about three 

 feet in diameter and three-fourths of an inch thick ; the sound emitted was feeble, 

 and the undulations continued 115 seconds, as deduced from the mean of six ex- 

 periments. 



In all these experiments, except the one in vacuum, tbe time of the cessation of 

 the tuniug fork was determined by bringing the mouth of a resounding cavity near 

 the end of the fork ; this cavity, having previously been adjusted to unison with 

 the vibrations of the fork, gave an audible sound when none could be heard by the 

 unaided ear. 



The tuning fork was next placed upon a cube of India rubber, and this upon 

 the mai'ble slab. The sound emitted in this case was scarcely that in the case of 

 the tuning fork suspended from the cambric thread; and frotn this anology of the 

 previous experiments we might at first thought suppose the time of duration would 

 be great — but this was not the case ; the vibrations continued only forty seconds. 



The question may here be asked what became of the impulses lost by the tuning 

 fork ? They were neither transmitted to the India rubber, nor given off to the air 

 in the form of a sound, but were probably expended in producing a change in the 

 matter of the India rubber, or were converted into boat, or both. Though the 

 inquiry did not fall strictly within the line of this series of investigations, yet 



