64 TjRAKSACTIOyS OF THE AMERICAN INSTITUTE. 



five and a-lialf times as long to convert a given quantity of water 

 into steam as to raise it from 32 deg. to 212 deg. This latent heat 

 would be enough to heat water, if a solid, red hot. If we add to 

 the pressure of the atmosphere, we shall have a higher temperature 

 of the steam ; hut the amount of latent heat in the steam will he 

 less, the sum of the latent and the sensible heat being a constant 

 quantity, equal to 1,180 deg. Fahrenheit. The conversion of water 

 into steam will expand it into 1,Y00 times its fonner bulk, and this 

 exerts a prodigious amount of mechanical force which is utilized in 

 the steam engine. Heat is nothing but a mode of motion ; and the 

 steam engine enables us to make that motion useful in the form of 

 mechanical power. [He illustrated the reconversion of motion into 

 heat by rapidly turning a brass tube containing ether and corked up, 

 and holding around it a wooden clamp until sufficient heat was 

 generated to convert the ether into vapor and blow the cork from 

 the tube.] Count E-umford, in the latter part of the last century, 

 tried a similar experiment upon a much larger scale. When in the 

 employment of the Bavarian government at Munich, he made those 

 remarkable experiments which have signalized his name in this 

 department of knowledge, for he employed horse power in the boring 

 of cannon held in a vessel of water at the ordinary temperature, not- 

 ing the time occupied, and the amount of force supplied. In about 

 two hours and twenty minutes he brought this large body of water into 

 a state of ebullition, simply by the mechanical power applied in bor- 

 ing ; and experiments have since demonstrated that in order to raise 

 a pound of water through one degree of Fahrenheit, there must be 

 sufficient power applied to raise one pound to the height of T72 feet. 

 This is what is called the mechanical equivalent of heat. [Prof. S. next 

 treated heated water in a closed spherical vessel connected with a 

 column of mercury and a thermometer. When the pressure of the 

 steam had forced the mercury to the height of thirty- three inches, 

 corresponding to a pressure a little more than twice that of the 

 atmosphere, the thermometer had risen to 245 degs. He then opened 

 a tube to allow the steam to escape into a vessel of water, at first 

 producing a rattling sound in consequence of the condensation of the 

 steam by the water, and the fiilling of the water to fill the space thus 

 left vacant ; but very soon the water was raised to the boiling point, 

 and then the rattling ceased, and the steam passed noiselessly througli 

 the water and escaped.] It is easy to convey heat in the form of 

 steam ; and it is now common to convey it in pipes sometimes for 



