324 Dynamic Theory. 



Thus suppose a kilogram starts upward with a velocity per second of 19. 6 

 metres. This speed then represents its energy of motion. At the end 

 of one second it will have gained an altitude of 14. 7 metres and will be 

 going only 9. 8 metres per second. This 9. 8 metres velocity, as shown 

 above, is good for an additional ascent of 4. 9 metres, so that at the end 

 of one second the kilogram has an energy of motion equal to 4. 9 kilo- 

 grammetres and an energy of position of 14.7, or 19.6 in all, just 

 what it started with. At the end of the second second it has reached a 

 hight of 19.6 metres and has ceased to move, all its energy being now 

 energy of position. As stated before, if the body falls down, all the 

 energy required to raise it up may be converted into heat. Experiments 

 have shown that if a kilogram were to fall 424 metres the energy de- 

 veloped would be sufficient to raise one kilogram of water one degree cen- 

 tigrade in temperature. One heat unit is therefore said to be equal to 

 424 units of energy or kilogrammetres. We thus see that a definite 

 amount of work or of the motion of a body in a mass is convertible into 

 an equivalent and equally measurable amount of heat or the motion of 

 matter by molecules. Heat is likewise convertible into molar or mass 

 motion, as shown in the expansive force of hot air and steam, &c. T f\\Q 

 hight of a body above the point to which it may possibly fall is called 

 its Potential. Mass x Potential = Work or Energy. The forms of En- 

 ergy which most affect organic beings will be discussed briefly in chap- 

 ters to follow, and the manner in which we have been influenced, differ- 

 entiated, controlled, and operated by them will be pointed out as far as 

 possible. It is entirely immaterial to my present purpose whether the 

 current theories of the several forms of energy are correct or not. For' 

 example, it makes no difference whether sound is the vibration of air, 

 iron, &c. , or the vibration of the hypothetical ether of which we shall 

 hear, or the effect of small particles of matter hurled from a sonorous 

 body. In any event it is the result of force of some sort, and a style of 

 force that has made its mark on animal life. In treating of these forces, 

 then, it will be best to use the most approved theories, and reserve crit- 

 icism to a later period. 



CHAPTER XXXVI. 



ELECTRICITY. 



If anyone will lay a piece of paper on the table and rub it vigorously 

 with the dry hand for a few moments, it will be found to be electrified 

 as well as somewhat heated. If it be pressed against the wall it will 

 hang there for some moments from the force of attraction. If it be 

 held near any light body, as a bit of cotton-lint or string, it will at- 

 tract it, and after holding it in contact with itself for a time it will re- 



