100 FIRST LAW OF GRAVITATION. 



as the tendency which those bodies have to fall to 

 the earth when not supported, and to remain on 

 its surface after they have fallen or when they 

 are once there, if not raised up by some other force 

 powerful enough for counteracting that tendency. 

 As this weight is, as we may say, a universal pro- 

 perty, it should be understood by even the most 

 unpretending observer, if he is to apply his obser- 

 vation to any useful purpose, how simple soever that 

 purpose may be. Its laws are as simple as itself 

 is universal ; and as they can be stated in very 

 plain language, every one should bear them in 

 mind. They are these : 



First, the tendency which any piece of matter 

 has to gravitate, or as it is termed, to fall, is exactly 

 in proportion to the quantity of matter in that 

 piece; and though its effects may be varied by 

 circumstances, in itself it remains unaltered. So 

 that, if the piece were broken into the greatest 

 number of smaller pieces, the amount of gravita- 

 tion in them would be exactly the same as that in 

 the large piece before it was broken. So also, if 

 any piece or pieces of matter be joined to another 

 piece or other pieces, the gravitation of the collec- 

 tion is always exactly equal to the sum of all the 

 gravitations of the individual parts. 



This property is indestructible ; and not only 

 forms part of the constitution of matter, but is the 

 property by means of which alone we acquire any 

 knowledge of matter at all. That which the 

 tongue tastes, or the nose scents, we cannot mea- 

 sure, or in anywise know but by inference ; and it 

 is by inference that we know what the ear hears, and 

 even what the eye sees, though after long practice 

 we take no notice of, and therefore forget, the pro- 



