52 
THE CANTOR LECTURE, 1890, 
The armature was a similar structure, but not wound with iron. The 
iron of the magnet weighed 7 lbs., and that of the armature 4*55 lbs. 
The weight was 2710 lbs., when excited by 16 of Sturgeon’s cast-iron 
cells. 
In a subsequent paper on the calorific effects of magneto-electricity, 
published in 1843, Joule described another form of electro-magnet of 
horse-shoe shape, made from a piece of boiler-plate. This was not 
intended to give great lifting power, and was used as the field-magnet 
of a motor. In 1852, another powerful electro-magnet of horse-shoe 
form, somewhat similar to the preceding, was constructed by Joule for 
. experiment. He came to the conclusion that, owing to magnetic 
saturation setting in, it was improbable that any force of electric 
current could give a magnetic attraction greater than 200 lbs. per 
square inch. “That is, the greatest weight which could be lifted by 
an electro-magnet formed of a bar of iron one inch square, bent into a 
semicircular shape, would not exceed 400 lbs.” 
With the researches of Joule may be said to end the first stage of 
development. The notion of the magnetic circuit which had thus guided 
Joule’s work did not commend itself at that time to the professors of 
physical theories : and the practical men, the telegraph engineers, were 
for the most part content to work by purely empirical methods. Be¬ 
tween the practical man and the theoretical man there was, at least on 
this topic, a great gulf fixed. The theoretical man, arguing as though 
magnetism consisted in a surface distribution of polarity, and as though 
the laws of electro-magnets were like those of steel magnets, laid down 
rules not applicable to the cases which occur in practice, and which 
hindered rather than, helped progress. The practical man, finding no 
help from theory, threw it on one side as misleading and useless. It 
is true that a few workers made careful observations and formulated 
into rules the results of their investigations. Amongst these, the 
principal were Ritchie, Robinson, Muller, Dub, Yon Koike, and Du 
Moncel; but their work was little known beyond the pages of the 
scientific journals wherein their results were described. Some of these 
results will be examined in my later lectures, but they cannot be dis¬ 
cussed in this historical resume, which is accordingly closed. 
