ON FORCE. 281 
out the assumption here made, M. Weber is obliged to suppose that 
the molecules of diamagnetic bodies are surrounded by channels, 
in which the induced molecular currents, once excited, continue 
to flow without resistance."* Diamagnetism and Magne-crystallic 
Action, p. 136-7. 
CHAPTER XVI. 
ON FORCE, f 
A SPHERE of lead was suspended at a height of 16 feet 
above the theater floor of the Royal Institution. It was 
liberated, and fell by gravity. That weight required a 
second to fall to the floor from that elevation; and the 
instant before it touched the floor it had a velocity of 32 
feet a second. That is to say, if at that instant the earth 
were annihilated, and its attraction annulled, the weight 
would proceed through space at the uniform velocity of 32 
feet a second. 
If instead of being pulled downward by gravity, the 
weight be cast upward in opposition to gravity, then, to 
reach a height of 16 feet it must start with a velocity of 32 
feet a second. This velocity imparted to the weight by 
the human hand, or by any other mechanical means, would 
carry it to the precise height from which we saw it fall. 
Now the lifting of the weight may be regarded as so 
much mechanical work performed. By means of a ladder 
placed against the wall, the weight might be carried up to 
a height of 16 feet; or it might be drawn up to this height 
by means of a string and pulley, or it might be suddenly 
jerked up to a heiglit of 16 feet. The amount of work 
done in all these cases, as far as the raising of the weight 
is concerned, would be absolutely the same. The work 
done at one and the same place, and neglecting the small 
change of gravity with the height, depends solely upon two 
things; on the quantity of matter lifted, and on the height 
to which it is lifted. If we call the quantity or mass of 
matter m, and the height through which it is lifted h, then 
the product of m. into h, or m h, expresses, or is propor- 
tional to the amount of work done. 
Supposing, instead of imparting a velocity of 32 feet a 
* In assuming these non-resisting channels M. Weber, it must be 
admitted, did not go beyond the assumptions of Ampere. 
j- A discourse delivered in the Royal Institution, June 6, 1863. 
