200 ANNUAL OF SCIENTIFIC DISCOVERY. 



the above numbers. After combination, the substance is in a state 

 of vapor, which sinks to 212 and afterward condenses to water. In 

 the first instance, the atoms fall together to form the compound ; in 

 the next instance, the molecules of the compound fall together to form 

 a liquid. The mechanical value of this act can be also calculated ; 

 nine pounds of steam in falling to water, generate an amount of heat 

 sufficient to raise 956X9=8, 614 pounds of water 1 Fahr. .Multiplying 

 this number by 772, we have a product of 6,718,716 foot-pound's (a 

 foot-pound is a pound raised one foot high) as the mechanical value of 

 the mere act of condensation. The next great fall of our nine pounds 

 of water is from the state of liquid to that of ice, and the mechani- 

 cal value of this act is equal to 993,56-1 foot-pounds. Thus our 

 nine pounds of water, in its origin and progress, falls down three 

 great precipices ; the first fall is equivalent to the descent of a tun 

 weight, urged by gravity down a precipice 22,320 feet high ; the second 

 fall is equal to that of a tun down a precipice 2,900 feet high ; and the 

 third is equal to the descent of a tun down a precipice 433 feet high. 

 I have seen the wild stone-avalanches of the Alps, which smoke and 

 thunder down the declivities with a vehemence almost sufficient to 

 stun the observer. I have also seen snowtiakes, descending so softly 

 as not to hurt the fragile spangles of which they were composed ; yet, 

 to produce, from aqueous vapor, a quantity of that tender mate- 

 rial which a child could carry, demands an exertion of energy compe- 

 tent to gather up the shattered blocks of the largest stone-avalanche 

 I have ever seen, and pitch them to twice the hight from which 

 they fall. Tyndall on Heat. 



Bodily Work and Waste. Every manifestation of physical force 

 involves the metamorphosis of a certain quantity of matter. Prof. 

 Houghton of Trinity College, Dublin, asserts, as the result of his 

 investigations, that, in the human organism, there is a definite rela- 

 tion between the amount of force exerted and the amount of urea 

 generated. The urea formed daily in a healthy man, weighing 150 

 pounds, fluctuates from 400 to 650 grains. Of this, 300 grains are the 

 result of vital work ; that is, of force expended in the motions of the 

 digestive organs and the heart, and in sustaining the temperature of 

 the body at a uniform rate. This amount exceeds all other ibrce gen- 

 erated and expended in the system, and is equal to that required to 

 raise 769 tuns one foot high. In addition to the mere act of living, 

 the working man undergoes bodily labor equivalent to lifting 200 tuns 

 one foot high daily, which requires the formation of 77*38 grains of 

 urea. The force expended in two hours hard mental labor involves 

 an expenditure of power equal to lifting 222 foot tuns, and a genera- 

 tion of urea weighing 86 grains. Thus we have a minimum formation 

 of urea during 24 hours amounting to 477,38 grains, for which there 

 is expended force equal to 969 foot tuns. 



Note. Urea is a colorless substance, which by slow evaporation 

 crystallizes in four-sided prisms. It consists of two atoms of carbon, 

 two of nitrogen, two of oxygen, and four of hydrogen. Its rational 

 formula has not been definitely settled. A little more than 46 per 

 cent by weight consists of nitrogen. It is through this important 

 compound that nearly all the nitrogen of the exhausted tissues of the 

 body are removed. According to Uecquerel, there is an excess of 



