434 ENERGY. 



Recapitulation. In this section we have considered 

 the Photographer's Camera and the human 

 Eye ; Microscopes and Telescopes ; the Magic 

 Lantern and the Stereoscope ; Polarization 

 of light by Absorption, by Reflection and by 

 Double Refraction. 



CONCLUSION. 



ENERGY. 



674. Varieties of Energy. Like matter, energy 

 is indestructible. "We have already seen that energy may 

 be visible or invisible (i. e., mechanical or molecular), 

 kinetic or potential. We have at our control at least 

 eight varieties of energy. 



(a.) Mechanical energy of position (visible, potential). 

 (&.) Mechanical energy of motion (visible, kinetic). 

 (c.) Latent heat (molecular, potential). 

 (d.) Sensible heat (molecular, kinetic). 

 '(e.) Chemical separation (molecular or atomic ; potential). 

 (/.) Electric separation (probably molecular, potential). 

 (g.) Electricity in motion (probably molecular, kinetic). 

 (h.) Radiant energy, thermal, luminous or actinic (molecular, 

 kinetic). 



675. Conservation of Energy. The doctrine 

 that, considering the universe as a whole, the sum of all 

 these forces is a constant quantity, is known as the Con- 

 servation, of Energy. 



a + b + c + d + e+f+g + fi = a. constant quantity. 



This does not mean that the value of a is invariable ; we 

 have seen it changed to other varieties as b or d. We have 



