THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



OCTOBER 1876. 



XXXII. On the Transformation of Gravity. 

 By James Croll, LL.D., F.R.S.* 



G 



]RA VITY in relation to Correlation. — Is gravity convert- 

 ible into other forms of energy ? Can gravity be con- 

 verted into beat, electricity, magnetism, &c. ? or can those 

 forms of energy be converted into gravity ? One, I presume, 

 may read all that has been written on correlation and conser- 

 vation of energy without finding a clear, distinct, and satis- 

 factory answer to the question. Few will admit that gravity 

 forms an exception to the great principle of correlation, stand- 

 ing isolated from all other forms of energy. It may be true 

 that gravity cannot be directly transformed into heat, elec- 

 tricity, magnetism, chemical affinity, &c, nor those forms 

 directly transformed into gravity ; but nevertheless the thing- 

 may be done indirectly. It is well known that if energy (no 

 matter under what form) can be converted into motion or 

 mechanical work, it can then be transformed into other forms 

 of energy. For example, if heat is made to perform mechani- 

 cal work, say to drive a machine, then that machine may be made 

 to generate electricity, and the electricity may in turn be con- 

 verted into other forms of energy. Or electricity may drive 

 the machine, then the machine may generate heat. The heat 

 is here not directly converted into electricity, nor the elec- 

 tricity directly into heat ; but it is done indirectly. The heat is 

 first converted into mechanical energy and then into elec- 

 tricity. The electricity is first converted into mechanical 

 energy, then into heat. Now gravitation will drive a machine 



* Communicated by the Author, having been read before the British 

 Association, September 1876. 



Phil Mag, S. 5. Yol. 2. No. 11. Oct. 1876. R 



