438 WRITINGS OF JOSEPH HENRY. [1874 



gave at first discordant sounds, and were found by their effect 

 upon an artificial ear to be considerably different in pene- 

 trating power; they were then adjusted by increasing or di- 

 minishing the space between the bell and the lower cylinder, 

 (by turning a screw intended for that purpose on the axis of 

 the bell,} until they produced the same effect upon the sand in 

 the membrane of the artificial ear ; but in order to be further 

 insured of the equality of the penetrating power of the sev- 

 eral whistles, the three steamers abreast — forming as it were 

 a platoon, were directed to proceed against the wind, sound- 

 ing all the time in regular succession, — the Cactus first, then 

 after an interval of a few seconds, the Mistletoe, and then 

 the Putnam, — until the stationary observers lost the sound 

 of each. They became inaudible all very nearly at the same 

 moment. The sound of the Putnam was thought to be 

 slightly less distinct; it was therefore chosen as a stationary 

 vessel, from which the observations of the sound of the other 

 two were to be made. 



The Putnam being anchored at the point before men- 

 tioned, arrangements were made for sending off the other 

 two vessels in opposite directions, one with and the other 

 against the wind, with instructions to return when the sound 

 became inaudible to those on the stationary vessel, this to 

 be indicated by a flag-signal. It should be mentioned that 

 the velocity of the wind was measured from time to time 

 during the subsequent experiments with one of Robinson's 

 hemispherical cup anemometers, made by Casella, of London. 

 The velocity of the wind as observed by this instrument 

 just before the starting of the vessels, was 6 miles per hour, 

 the instrument being freel}'' exposed on the paddle-boxes of 

 the steamer. A sensitive aneroid barometer marked 30395 

 ins. and continued to rise gradually during the day to 30'43 

 ins.; the temperature was 71° F. 



1st trial. — The vessels left at 11:18 a. m., the wind being from 

 the west, Captain Davis taking charge of the sounding of the 

 whistle on the Cactus, which proceeded east with the wind, 

 the sound coming to the ear of the observer against the wind ; 

 while the sounding on the Mistletoe was in charge of Gen- 



