KENNELLY AND UPSON— HUMMING TELEPHONE. 



331 



The distance between the faces of the two instruments could be 

 varied at will by pulling out, or pushing in, the telescoping tube- 

 sections. The average current in the primary circuit was measured 

 with a Weston d.c. milliammeter. The pitch of the humming note 

 was measured approximately by the ear, with the aid of a number 

 of short organ pipes, and, in some instances, with the aid of a violin. 

 The voltaic battery used consisted of a selected number (from two 

 to nine, but usually four) of 25-ampere-liour lead storage cells. The 

 reversing switch in the secondary circuit enabled the receiver ter- 

 minals to be reversed at will. 



Transmitter. 



Receiver. 



Fft 



Tutie Length 



nH'flmmeter 



Hililili— 



Battery. Induction Coil. Reversing Snitch. 



Fig. I. Diagram of Humming Telephone Connections. 



The Telescoping Tubes. — The tubes were made of heavy wrap- 

 ping paper. Their internal diameters varied from 5 cm. (2 in.) to 

 6 cm. (2 J in.). They were used in lengths of 65 cm. (25^ in.), 

 with a few shorter and longer sections for special measurements. 

 The substance of which the tubes was composed did not appreciably 

 affect the observations. It was found, however, that if the tele- 

 scoping sections did not fit fairly tightly, erratic results were ob- 

 tained. Closely fitting sections were used. 



The Transmitters. — The transmitters used were of the standard 

 Western Electric- Co. type and manufacture. The diaphragm in 

 these instruments was of aluminum, 6.32 cm. (2.49 in.) in total 

 diameter, and 0.55 mm. (0.022 in.) thick, over a coating of Japan 

 varnish on one face. The diaphragm was loaded at its center with 

 one of the disk electrodes of the carbon microphone. The dia- 

 phragm was damped by being clamped between rubber rings to an 



