CHAP. V.] OPENING MANHOOD 1847 TO 1850. Ill 



chemical affinity, which are all convertible into one another 

 and affect all bodies. 



The third kind acts between the particles of the same 

 body, and tends to keep them at a certain distance from one 

 another and in a certain configuration. 



When this force is repulsive and inversely as the dis- 

 tance, the body is called gaseous. 



When it does not follow this law there are two cases. 



There may be a force tending to preserve the figure of 

 the body or not. 



When this force vanishes the body is a liquid. 



When it exists the body is solid. 



If it is small the body is soft ; if great it is hard. 



If it recovers its figure it is elastic ; if not it is inelastic. 



The forces in this third division depend almost entirely 

 on heat. 



The properties of bodies relative to heat and light are 



Transmission, Eeflection, and Destruction, 

 and in the case of light these may be different for the three 

 kinds of light, so that the properties of colour are 

 Quality, Purity, and Integrity ; or 

 Hue, Tint, and Shade. 



We come next to consider what properties of bodies may 

 be perceived by the senses. 



Now the only thing which can be directly perceived by 

 the senses is Force, to which may be reduced heat, light, 

 electricity, sound, and all the things which can be perceived 

 by any sense. 



In the sense of sight we perceive at the same time two 

 spheres covered with different colours and shades. The 

 pictures on these two spheres have a general resemblance, 

 but are not exactly the same ; and from a comparison of the 

 two spheres we learn, by a kind of intuitive geometry, the 

 position of external objects in three dimensions. 



Thus, the object of the sense of sight is the impression 

 made on the different parts of the retina by three kinds of 

 light. By this sense we obtain the greater part of our 



