200 



Proceedings of Indiana Academy of Science 



Mouthpiece by suspending a small disc flatwise in the mouth of the 

 horn as indicated in figure 1, a, so that all pulses striking the diaphragm 

 would suffer one reflection, and therefore equal retardation. This im- 

 provement eliminates a large part of the buzzing and muffled tones 

 common in telephones. 



The arrangement of the apparatus used for taking the data in this 

 report is indicated in figure 2, and is a modification of the "hook-up" 

 employed by the Kellogg Switchboard and Supply Company in their 

 common battery telephones.' A, A' are telephone transmitters, shown in 

 the diagram with the ordinary flared horn; R, R' are adjustable re- 

 sistances, R having a capacity of about 50,000 ohms and R' about 10,000 

 ohms; L, L' are induction coils (small telephone coils with cores) ; C is a 



Fijr. 2. Hook-up for Iho cxpcriniriil. 



^ V//////y/y/y/////////////y , 



C 



a 



'-'• ,'^ ,o. 



V4- -r 





/V 



v^ 



y^////////////////////T77y(/, 



/. 



■^k. 



K 



Fitr. '■>. Heatin.!:; oven for Knipp Tube. 



1/3 m. f. condenser; T a Baldwin mica-disc receiving set; B, B' are 2 

 volt storage cells ; and S is a double throw switch arranged so that either 

 transmitter could be instantly thrown into the circuit. 



In figure 3 are shown the details of the heating oven for the Knipp 

 Singing Tube. M is a coil of three or four turns of No. 28 nichrome 

 wire and was heated on the 110 volt circuit with about 5 amperes of 

 current. The walls of the oven were made of a.sbestos sheeting, such as 

 is ordinarily used to cover steam pipes, from which the hemp and 

 sisal body had previously been burned so that it would not stain the 

 glass tube. Knipp Tubes were chosen for the experiment because they 

 came more nearly than any other sounding instrument to giving a point 

 source of sound, while tests have shown that the tones" given off by 



■* "Principles of the Telephone," p. 99, by Jansky and Faber. 

 -' New Standard of Sound Enersy. C. T. Knipi). Phys. Rev. 

 155-156. 



Feb., 1920. 



