.S7A- U'lI.LIAM SIEMENS, l-.R.S. 53 



himself, might probably have arrived sooner at a practically useful 

 iv>ult, but he might claim for himself at least that strong con- 

 viction, approaching enthusiasm, which alone could have given 

 him strength to combat successfully the general discouragement 

 and the serious disappointments he had met with. 



The following illustrations, proving the imperishable nature of 

 physical forces and their mutual convertibility, were made use of 

 to indicate more clearly the principles his engine was based upon. 



A weight falling over a pulley, to which it was attached by a 

 siring, would impart rotary motion to a fly wheel, fixed upon 

 the same axis with the pulley, and the velocity imparted to the 

 wheel would cause the string to wind itself upon the pulley, till 

 the weight had reached nearly its original elevation. If the 

 friction of the spindle and the resistance of the atmosphere could 

 be dispensed with, the weight would be lifted to precisely the 

 same point from whence it fell, before the motion of the wheel 

 was arrested. In descending again, it would impart motion to the 

 wheel as before, and this operation of the weight, of alternately 

 falling and rising, could continue adinfiniium. If the string were 

 cut at the instant when the weight had descended, the rotation of 

 the wheel would continue uniformly, but it might soon be brought 

 to a stop by immersing it in a basin filled with water. In this 

 case the water was the recipient of the force due to the falling 

 weight, residing in the wheel ; and by repeating the same ex- 

 periment a sufficient number of times, we could find an increase of 

 temperature in the water, a fact discovered by Joule, in 1843, 

 which first proved the identity of heat and dynamic effect, and 

 established their numerical relation. If the weight falling over a 

 pulley were one pound, and the distance through which it fell one 

 foot, then each impulse given to the wheel would represent one 

 foot pound, the commonly adopted unit of force ; and if the water 

 contained in the basin weighed also one pound, it would require 

 770 repetitions of the experiment of arresting the wheel in the 

 water, before the temperature of that water was increased by one 

 degree Fahrenheit. 



Another illustration made use of, was that of a hammer falling 

 in vacua upon a perfectly elastic anvil. The hammer would, under 

 these circumstances, rebound to precisely its original elevation, and 

 granting the perfect elasticity of both hammer and anvil, neither 



