SCIENTIFIC TRACTS 



NUMBER IV. 



GRAVITATION. 



INTRODUCTORY REMARKS. 



PERHAPS the reader, on seeing the title of this tract, 

 will be disposed to doubt whether the subject is a use- 

 ful or interesting one. We all know, it may be said, 

 that bodies fall towards the earth, and what can philoso- 

 phers teach us in addition to this simple knowledge of 

 the fact, than merely to give to the generalojaw, the 

 learned name of Gravitation? Giving a name* is no ex- 

 planation, i. 



Let us attend one "moment to what is meant by an ex- 

 planation. A savage sees,; a sailor, who has landed on 

 his shores, point his gun towards the wild animal, bound- 

 ing through the forest. A flash and an explosion suc- 

 ceed, and the animal stops* suddenly in his progress, 

 falls bleeding to the ground, and dies. If the aston- 

 ished native ask- an explanation, he is told that the in- 

 strument which produced the/effect is hollow; that it 

 contained an explosive powder and a heavy ball ; that 

 the gunner's finger, by a motion too small' for him to per- 

 ceive, produced a collision of ftint and st'eel, and that, 

 by the resulting spark, the charge is inflamed, and the 

 ball is forced through the air, with a rapidity which his 

 eye cannot follow, and which is fatal to the object of its 

 aim. 



This is one kind of explanation. It consists, as every 

 one will easily see, of bringing to view circumstances 

 which intervene between the cause and the effect.; and 

 which, before, were hidden. The pointing of the p~un is 

 the cause, the death of the animal the effect, and the 

 collision of the flint and steel, the explosion ofthepow- 



VOL. i NO. iv. 7 



