58 Prof. J. C. Bose on a Complete Apparatus f of 



obtained by making the radiating spheres very small. The 

 shortest wave-length produced is about 6 mm., and the corre- 



Fig. 1.— The Kadiator. 



sponding number of oscillations is about 50,000 millions in a 

 second. The frequency of vibration in this case will be seen 

 to be about thirteen octaves lower than that which produces 

 visible radiation. The intensity of radiation in the above 

 case is rather feeble, and I use in general electric waves of 

 about half an inch in length. 



The jointed electrodes carrying the beads are in connexion 

 with a small modified Ruhmkortf' , s coil, actuated by a small 

 storage cell. The usual vibrating interrupter is generally a 

 source of trouble ; the contact points get worn out, and the 

 break becomes irregular. The great objection (as Hertz 

 found) to the continuous production of secondary sparks is 

 the roughening of the surface of the radiating ball, by which 

 the spark ceases to be oscillatory. It is very troublesome, in 

 the middle of aji experiment, to be obliged to take out the 

 radiator for polishing. The flash of radiation produced by a 

 single break is enough for an experiment, and it is a mere 

 waste to have a series of useless oscillations. In my apparatus 

 for quantitative measurements I have therefore discarded the 

 vibrating interrupter in favour of a simple break- key. To econ- 

 omize space, I wind the condenser (a long stiip of paraffined 

 paper with tin foils on opposite sides) round the secondary of the 

 coil, appropriate connexions being made with the interrupting 

 key. The coil and a small storage cell are enclosed in a metal 

 box, in accordance with the precautions which Prof. Lodge 

 had found to be necessary. I used tinned iron in order to 

 screen the space outside from magnetic disturbances due to the 

 making or breaking of the primary circuit of the coil. A sudden 

 magnetic variation disturbs the receiver. The iron box is 

 placed inside a second box of thick brass or copper. These 

 precautions are taken to prevent straying of electric radiation. 

 Through a small opening in the back or side of the box the stud 

 of the press-key projects. In front of the box is the radiator- 

 tube,, which may be square or cylindrical. Inside this tube is 

 mounted the radiating originator. A flash of electric radiation 

 is produced by a proper manipulation of the interrupting 



