572 Intelligence and Miscellaneous Articles. 



ON A SIMPLE AND VERY ACCURATE METHOD OF TUNING TWO 

 FORKS TO UNISON. BY ROBERT SPICE, F.C.S. 



Though the optical method of tuning, of Lissajous, gives good 

 results, I find that two forks thus tuned to unison may be & fraction 

 of a vibration out, without in any way disturbing the steadiness of 

 the figure. 



In the 2nd edition (English) of TyndalTs 'Sound,' in Lecture VII., 

 the author says, " I divido this jar by a vertical diaphragm, and 

 bring one of the forks over one of its halves, and the other fork 

 over the other. The two semicylindors of air produce beats by 

 their interference. On removing the diaphragm, the beats continue 

 as loud as before, one half of the same column of air interfering 

 with the other." 



Dr. Tyndall does not, however, mention the fact that precisely 

 the same result would have been obtained if no diaphragm had been 

 employed ; yet this is so. When two unison forks are struck on the 

 knee (or by a piece of lead covered with leather) and then held 

 tor/ether over their proper resonant column, the following phenomena 

 will be observed. 



If there is a difference between their rates of several vibrations, 

 there will of course be rapid beats ; if the forks are very nearly in 

 tune, the beats will succeed each other at long intervals ; further, 

 when they are almost perfectly in tune, there will not be any beats 

 properly so called, but after the sound of the forks has nearly died 

 away, it will rise or swell out again very slightly, proving that there 

 had been interference. 



Finally, when the forks are absolutely alike, there will be a gra- 

 dual decrease of sound, down to silence, without any reinforcement 

 at any time. 



I find that, to carry out this tuning absolutely, both forks must 

 be at the same temperature ; consequently, after using a file on one 

 of them, I place both forks in a vessel of water to equalize their 

 temperatures, wipe them dry, and test them. To show the accuracy 

 of this method, I select the following example : — 



A pair of Ut 3 forks (256 vibrations) will sound over a column for 

 about 135 seconds. Suppose that the sound decreases up to the 100th 

 second, and then begins to rise ; obviously 100 seconds is the time 

 of half a heat, or 200 seconds the beating-time ; that is to say, it 

 will have been demonstrated that one of the forks gave -g-jj-o of a 

 vibration per second more than its fellow. 



"What has been said of the unipon applies to other intervals. 



I have recently executed by this method Ut 4 , Ut 5 , Ut 6 , and Ut 7 

 forks for the physical cabinet of Columbia College. — Silliman's 

 American Journal, May 1876. 



230 Bridge Street, Brooklyn, Jan., 1876. 



