414 WRITINGS OF JOSEPH HENRY. [1856 



upon a sounding-board ; placing a tuning-fork on the wood 

 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 upon 

 the board. 



A tuning-fork suspended from a tine cambric thread and 

 vibrated in air was found, from the mean of a number of 

 experiments, to continue in motion 252 seconds. In this 

 experiment, had the tuning-fork been in a perfect vacuum 

 suspended without the use of a string, and further, had there 

 been no setherial medium, the agitation of which would give 

 rise to light, heat, electricity, or some other form of setherial 

 motion, the fork would have continued its vibration for- 

 ever. 



The fork was next placed upon a large, thin pine board — 

 the top of a table. A loud sound 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 against a partition of this mate- 

 rial a loud sound would have been heard in the adjoining 

 room; and 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 so 

 great an amount of the motive power of the fork being com- 

 municated to a large mass of wood. The increased sound 

 was due to the increased surface. In other words the short- 

 ness of duration was compensated for by the greater intensity 

 of efifect produced. 



The tuning-fork was next placed upon a circular slab of 

 marble about three feet in diameter and three-quarters of an 

 inch thick. The sound emitted was feeble, and the undula- 

 tions continued one hundred and fifteen seconds, as deduced 

 from the mean of six experiments. 



In all these experiments, except the one in a vacuum, the 

 time of the cessation of the motion of the tuning-fork was 

 determined by bringing the mouth of a resounding cavity 



