TRANSACTIONS OF SECTION A. 603 



system or to change any system of lightning protection without actual experience 

 upon a large scale. 



Sir William Thomson said : In respect to the very central difTerence between 

 Mr. Oliver Lodge and Mr. Preece, he might say he thought My. Oliver Lodge was 

 in the American stage with reference to judging the functions of inertia, and Mr. 

 Preece rather in the English stage. They call it ' keeping our station ' in England, 

 but the Americans called it ' keep going ahead.' These are the two functions of 

 inertia to prevent anything from getting into motion, and when in motion to keep 

 it going ; and both those functions were plain in this electrical influence, lie could 

 not but think that if Mr. Lodge continued his work he would find theexplanation 

 of the very great discovery that he has made, namely, that iron wire aftbrds a better 

 discharger, or an easier path in the circumstances M"r. Lodge had minutely defined, 

 than does copper. He hoped Mr. Lodge would pursue the investigation, keeping 

 the circumstances in all respects as similar as possible— comparing, for instance, a 

 thin iron wire with a thin lead or brass wire of precisely the same ohmic conductivity. 

 He knew that that gentleman had done a good deal already, but a good deal more 

 might need to be done, and all that could be done by experiment could be done in 

 a very easy investigation. The other point Dr. Oliver Lodge very importantly 

 accentuated, namely, that the energy must be got quit of somehow and some- 

 where— it must be got quit of either "in the conductor or elsewhere. If got quit of 

 in the conductor, then there must be energy to melt the conductor, and it might 

 be a positive advantage to have quasi-inertia to keep it oscillating for a time instead 

 of volatilising the conductor in an instant. He did not hazard that in the slightest 

 degree as an explanation, but it was certainly something that must be taken into 

 account in connection with the experimental result which Mr. Lodge had put 

 before them. 



It was interesting to hear about the number of horses placed in a row, the first 

 and last of the row being killed and the others not touched by a lightning discharge, 

 which seemed to pass through them all. A very common lecture-room experiment 

 •was to give a Leyden jar shock to a hundred or two hundred students sitting 

 on the benches, making them all join hands. He had no doubt that those students 

 next to the ends of the line experienced the shock much more potently than those 

 in the middle of the line. There was one very marked influence here, and that vyas 

 want of perfect insulation ; but there was another— self-induction. Self-induction 

 was now in the air — they thought of nothing else in fact — and some of them thought 

 of self-induction incessantly in these matters. He thought that the extent of self- 

 induction might be tried, and that it would be a very interesting experiment. He 

 thought they must also try this same experiment with as nearly as possible similar 

 insulation with a number of people spreading out in a large circle. Then the self- 

 induction would be much more influential in causing the discharge not to keep 

 through the line of comparatively good conducting bodies. Take the case of 

 persons ranged in a row taking an ele^ctrical shock ; if the row is zigzag then self- 

 induction will not have the same tendency to cause the lightning discharge to leave 

 the line of the best conductors as it will have if the conducting bodies are placed in 

 a wide circuit. Then ho believed the imperfect insulation of standing on the floor 

 would be much more potf^nt, and he should expect that those who were_ in the 

 middle of the row would experience a shock much less in the case of standing in a 

 wide circle than in the case of standing on similarly good conducting material in a 

 zigzag row. At all events that would be an experiment worth repeating. 



Mr. Preece had spoken of the impossibility of conceiving of the enormous 

 augmentation of potential in the.se actions. Take the word inertia which Mr. 

 Preece used and the judiciousness of which he fully agreed with and apply it to the 

 steam hammer and the hydraulic ram. They applied a comparatively gentle force 

 to a steam hammer untilit produced an exceedingly intense action a,t the blow. 

 Take a hydraulic ram again, the well-known analogue for getting up a high potential 

 by self-induction in an electric circuit, and he thought they would see that Professor 

 Lodge's explanation of the phenomena he had brought before them was altogether 

 valid and not very difficult to work out in detail. 



Exceedingly interesting questions had been put and remarks made in respect to 



