Psf/c/iotogi'ral /tiirntif/atiotm 215 



A. I'SYCHuMETHtO TNHTHUMENTS 



1 think it will In- l)eHt in dciilinj; with Francis Onlton's psyche )rn«'tric wurk 

 to start with soinn ucrount of the instrunu'nts devised by him. In I 87<> there- 

 was exhibited at South Kensington a "Special Loan (collection of Scientific 

 Appaiiittis," and in connection witli this exhibition a series of conferences 

 was held in the month of May. At these conferences di.scnssions on various 

 subjects took place, largely in relation to the instruments exhibited. Spottis- 

 woodti \vi\H J'resident of the .section of Physics, ami among the Vice-Presi- 

 dents were he la line, llelmholt/,, Tyndall and Sir William Thomson (Lord 

 Kelvin). On May 19, one of the subjects for discussion was "Tlie Limits of 

 Audible Sound," and among other papers Galton gave an account of his 

 "Whistles for determining the uj)per limits of amlible .scmnd in ditterent 

 persons'." 



Galton notes that the number of vibrations perceived oJ' a "clo.soil pipe" 

 or whistle depends upon its length. Accordingly he alters its length by a 

 screwed plug at the closed ends; the ntmil)er of turns and part turns of the 

 screw are registered on a scale fixed to the walls of the whistle and on the 

 screw head. The j)itch of the screw is 25 to the nich. Hence one turn of tlie 

 head shortens the tube by 2"g-th of an inch and the head of the screw l)eing 

 divided into ten parts it is possible to shorten the wliistle by ^^ of an inch 

 with perfect ease. Now the velocity of sound in ordinaiy conditions of 

 temperature and pressui-e being 13,440 inches per second, the note of the 

 whistle may be found by dividing 13,440 by four times the length in inches, 

 i.e. by 4h x^Jir. where n is the reading on the scale, or 840,000/n is the 

 number of vibrations per seconds For example, if the screw lie set at 10, 

 there are 84,000 vil)rations a second, if at 70, 12,000, while a setting of 

 120 denotes 7000 vibrations per second. This rule of course ajjplies only to 

 strictly longitudinal vibrations. (}alton very properly observes that it ceases 

 to apply when the length of the tube is less than one-and-a-half times its 

 diameter. When the tube is reduced to a shallow pan, it is the transverse 

 vibrations which are all important. The necessity of preserving a fair pro- 

 portion between diameter and length, led (ialton to reduce the bore of his 

 tube in some cases to a very minute dimension. On this account he con- 

 sidered that his whistles could not be relied on for vibrations of more than 

 14,000 to the second. 



CJalton notes than when the limits of audibility for a given person are 

 reached "the sound usually gives place to a peculiar sens;ition, which is not 

 sound but more like dizziness, and which some persons experience in a high 

 degree." He further remarks that young people hear shriller sounds than 



' K>outh Keimint/ton Afii.ieum Conferences held in connection with the Special Loan Col- 

 lection of Scientijic Apparatus, 1876. Physics anil Mechanics Volnme, p. 61. Publishe<l by 

 Clmpman iiiul Hall. Gallon's account was reproduced with some intro«luctory matter in a 

 pamphlet cntitlixi "Galtons Whistles," issued by Tisley and Co., who manuractured the 

 whistles coinniercially. They are still manufactured, but not by this firm's successors. 



'' The original gives 8-t,000/n by a slip. 



