54 Dr. 0. Lodge on Electric Radiation. 



impulses. Another, but almost microscopic, recording needle 

 with a period of ^ second might also be suspended. 



The charge on the oscillator used in the present set of 

 experiments vibrates 300 million times a second, which, though 

 slower than the electric quiverings on, say, a three-inch ball, 

 is yet quick enough to demand care and attention. 



With very large oscillators, such as that described at the 

 beginning of this paper, no such minute precautions need be 

 taken. 



Fig. 4. —Small Oscillator used for optical experiments. Scale |. 



Plates 8 centim. diameter. 



Knobs 2 centim. diameter. 



Each rod 6 centim. long and 1 centim. diameter. 



Spark-gap about 8 milliin. 



S 

 Static capacity, — =1*4 centim. 



Self-induction, ii =190 „ 



Characteristic factor, log — =4*5. 

 a 



Rate of vibration, 300 million per second. 

 Wave-length, 1 metre. 

 Dissipation-resistance, 7250 ohms. 

 Initial stock of energy, about 5400 ergs. 

 Power of initial radiation, 128 horse-power. 

 Number of vibrations before energy would be at this rate 

 dissipated, about 1^. 



My oscillator is a good deal dumpier, and its ends have 

 more capacity, than those of corresponding wave-length used 

 by Hertz ; the reason being that I prefer to make the electro- 

 static capacity bear a fair relation to the electromagnetic 

 inertia, so as to gain a reasonable supply of initial energy 

 for radiation. The store of energy is proportional to the 

 capacity ; the rate at which it is radiated per second is 

 independent of it. Large terminal capacity helps to preserve 

 a high potential longer, and so prolongs the duration of the 

 discharge. 



The wave-length of the emitted radiation is easily calculated 

 approximately from the expression 



