14 ANNIVERSARY ADDRESS. 
In connection with electrical appliances, I may mention the 
friendly rivalry that was going on at the time of my stay in 
England between the President of the Royal Society (Mr. 
‘Spottiswoode) and Mr. Warren De La Rue—a rivalry unfortu- 
nately brought to a close soon afterwards by the lamented death 
of the former. These gentlemen were studying (among other 
electrical phenomena) the discharge through vacuous tubes, and 
for this purpose electricity of pretty high tension is required. 
Mr. Spottiswoode used induced electricity, and he had made for 
him the largest induction coil ever constructed. It had a primary 
coil of 660 yards, enclosing a core of iron wire weighing 67 lbs., 
and the secondary wire measured 280 miles. With thirty Grove 
cells this coil gave a spark 42 inches long. This powerful machine 
was ruined (as I understood) at the Paris Exhibition. He after- 
wards got an induction machine of the Topler variety, consisting 
of 85 pairs of ebonite plates, about 2 feet in diameter. I saw 
this in action, and it gave a splendid rush of sparks. Mr. 
Spottiswoode showed me also a large magneto-electric machine 
that he was getting made for the same experiments. 
Mr. De La Rue, on the other hand, sought to compass the 
same ends by battery electricity, and to obtain the necessary 
tension he had to multiply cells to a great extent. He invented 
the chloride of silver battery, in which the elements are chloride 
of silver and zinc, immersed in solution of sal ammoniac enclosed 
in a small test tube. Each cell hasan E.M.F. of 1 volt. He 
continued to add cells to this battery until at the time I saw it 
there were no fewer than 15,000. This number gave a spark three- 
quarters of an inch long. 
One of the pieces of apparatus that I was commissioned to 
get for the University was a polariscope of large size. My 
instructions were to get the largest Nicol prisms procurable, 
and my hunt after these was troublesome but at the same 
time interesting. I applied to all the principal dealers in these 
articles, and could find no prisms with so much as 2 inches 
aperture. I consulted with Professor Adams, of King’s College, 
Maer payee 
