526 Prof. A. GL Bell on the Production of 



receiver (G), which was so arranged that the lampblack surface 

 exposed was limited by a slit, as shown. 



Under these circumstances sounds were obtained in every 

 part of the visible spectrum, excepting the extreme half of the 

 violet, as well as in the ultra-red. A continuous increase in 

 the loudness of the sound was observed upon moving the re- 

 ceiver (G) gradually from the violet into the ultra-red. The 

 point of maximum sound lay very far out in the ultra-red. Be- 

 yond this point the sound began to decrease, and then stopped 

 so suddenly that a very slight motion of the receiver (G) made 

 all the difference between almost maximum sound and complete 

 silence. 



(2) The lampblacked wire gauze was then removed, and 

 the interior of the receiver (G) was filled with red worsted. 

 Upon exploring the spectrum as before, entirely different re- 

 sults were obtained. The maximum effect was produced in 

 the green, at that part where the red worsted appeared to be 

 black. On either side of this point the sound gradually died 

 away, becoming inaudible on the one side in the middle of 

 the indigo, and on the other at a short distance outside the 

 edge of the red. 



(3) Upon substituting green silk for red worsted, the 

 limits of audition appeared to be the middle of the blue and 

 a point a short distance out in the ultra-red. Maximum in 

 the red. 



(4) Some hard-rubber shavings were now placed in the re- 

 ceiver (G) . The limits of audibility appeared to be, on the one 

 hand, the junction of the green and blue, and, on the other, the 

 outside edge of the red. Maximum in the yellow. Mr. Tainter 

 thought he could hear a little way into the ultra-red ; and to 

 his ear the maximum was about the junction of the red and 

 orange. 



(5) A test-tube containing the vapour of sulphuric ether 

 was then substituted for the receiver (G). Commencing at 

 the violet end, the test-tube was gradually moved down the 

 spectrum, and out into the ultra-red, without audible effect ; 

 but when a certain point far out in the ultra-red was reached 

 a distinct musical tone suddenly made its appearance, which 

 disappeared as suddenly on moving the test-tube a very little 

 further on. 



(6) Upon exploring the spectrum with a test-tube contain- 

 ing the vapour of iodine, the limits of audibility appeared to 

 be the middle of the red and the junction of the blue and 

 indigo. Maximum in the green. 



(7) A test-tube containing peroxide of nitrogen was substi- 

 tuted for that containing iodine. Distinct sounds were ob- 



