Faraday as a Discoverer. 43 
that this paper on vibrating surfaces was too heavily laden with 
experiments. 
Discovery of Magneto-electricity : Explanation of Arago’s Magnetism of 
Rotation: Terrestrial Magneto-electric Induction: The Extra Current, 
The work thus far referred to, though sufficient of itself to 
secure no mean scientific reputation, forms but the vestibule 
of Faraday’s achievements. He had been engaged within these 
walls for eighteen years.* During part of the time he had 
nk in knowledge from Davy, and during the remainder he 
continually exercised his capacity for independent inquiry. In 
1831 we have him at the climax of his intellectual strength, 
forty years of age, stored with knowledge and full of original 
power. Through reading, lecturing, and experimenting, he 
had become thoroughly familiar with electrical science: he saw 
where light was needed and expansion possible. The phenomena 
of ordinary electric induction belonged, asit were, to the alpha- 
bet of his knowledge ; he knew that under ordinary circum- 
stances the presence of an electrified body was sufficient to 
excite, by induction, an unelectrified body. He knew that the 
wire which carried an electric current was an electrified body, 
and still that all attempts had failed to make it excite in other 
le knew well that from every experiment issued a kind of ra- 
diation, luminous in different degrees to different minds, and 
rdly trusted himself to reason upon an experiment that 
he had not seen. In the autumn of 1831 he began to repeat 
__* He used to say that it required twenty years of work to make a man in Phys- 
ical Science ; the previous period being one of infancy. 
