GRAVITATION. 85 



ableness of this principle in its operation. Some very 

 important consequences however result from them, and 

 all the effects produced by gravitation depend upon them. 

 They consequently deserve, each, a separate considera- 

 tion. 



1, It cannot be interrupted or changed. 



A stone falls towards the earth as rapidly when some 

 substance is below it, intervening between it and the 

 earth, as without such intervention. In other words, 

 nothing can cut off the communication between one body 

 and another, so as to interrupt the gravitating force which 

 tends to bring them together. If, in the case of the tor- 

 sion balance, a plate of brass, or of any other substance, 

 is brought between the two bodies with which the experi- 

 ment is tried, it will not in the least degree interfere with 

 their action. It may perhaps at first view, appear that 

 no one would have expected such an interference. We 

 should naturally have supposed, it may be said, that the 

 interposition of a foreign substance would not cut off the 

 communication. But this impression results from long 

 familiarity with the fact. Young persons are always 

 surprised to see a penknife attracting a magnetic needle 

 through the glass or the wood of the case ; and an ex- 

 cited electric causing the leaves of the electrometer to 

 diverge, when the instrument is enclosed in an air-tight 

 glass case, is often exhibited to a class in Philosophy as a 

 wonderful phenomenon. No reason can be assigned, 

 why the attraction of gravitation should act through an 

 intervening substance, more than that of electricity and 

 magnetism, or why the mind, which is surprised at it in 

 the former case, should consider it a matter of course in 

 the latter.* 



As the gravitating power of matter cannot be cut off, 



* The attraction of magnetism is cut off by the interposition of au 

 iron plate. A curious subject, of a moment's reverie, may be fur- 

 nished by reflecting on the complete revolution in the arts and the 

 business of life, which would be produced by the discovery of a sub- 

 stance, which would in the same manner interrupt gravitation, an4 

 thus enable man to destroy weight at his pleasure. 

 VOL. I. NO. IV. 8 



