Sound by Radiant Energy. 523 



Distance from Focal Point of Lens at which Sounds become 

 Inaudible with Different Substances. 



millim. 



Zinc diaphragm (polished) 1*51 



Hard-rubber diaphragm 1*90 



Tin-foil „ ' 2-00 



Telephone „ (japanned iron) „ 2*15 



Zinc „ (unpolished) 2*15 



White silk (in receiver shown in fig. 1) 3'10 



White worsted „ „ „ 4-01 



Yellow worsted „ „ „ 4*06 



Yellow silk „ ,, „ 4*13 



White cotton-wool „ „ „ 4*38 



Green silk „ „ „ 4*52 



Blue worsted „ „ „ 4*69 



Purple silk „ „ „ 4' 82 



Brown silk ,, „ „ 5*02 



Black silk „ „ „ 5*21 



Bed silk „ „ „ 5*24 



Black worsted „ „ ,, 6*50 



Lampblack. In receiver the limit of audibility could 



not be determined on account of want of space. 



Sound perfectly audible at a distance of - 1O00 



Mr. Tainter was convinced from these experiments that this 

 field of research promised valuable results ; and he at once de- 

 vised an apparatus for studying the effects, which he described 

 to me upon my return from Europe. The apparatus has since 

 been constructed ; and I take great pleasure in showing it to 

 you today. 



(1) A beam of light is received by two similar lenses (A, B, 

 fig. 10*), which bring the light to a focus on either side of 

 the interrupting-disk (C). The two substances whose sonorous 

 powers are to be compared are placed in the receiving vessels 

 (D, E) (so arranged as to expose equal surfaces to the action 

 of the beam) which communicate by flexible tubes (F, G) ? of 

 equal length, with the common hearing-tube (H). The re- 

 ceivers (D, E) are placed upon slides, which can be moved 

 along the graduated supports (I, K). The beams of light pass- 

 ing through the interrupting-disk (C) are alternately cut off by 

 the swinging of a pendulum (L). Thus a musical sound is 

 produced alternately from the substance in D and from that 

 in E. One of the receivers is kept at a constant point upon 

 its scale ; and the other receiver is moved towards or from the 

 focus of its beam until the ear decides that the sounds pro- 



[* The letters in this figure were omitted by the author, and the omission 

 unfortunately was not detected until after the Plate was printed ; the 

 reader can easily supply them. — Ed. Phil. Jfcry.] 



