NATURAL PHILOSOPHY. 161 



and mechanical force, has extended his researches to the heat emitted by the 

 sun ; and he observes that this heat corresponds to a development of mechan- 

 ical force, which, in the space of about 100 years is equivalent to the whole 

 active force required to produce the movement of all the planets. The author 

 examines successively the different sources of heat, and ends by concluding 

 that the solar heat can have no other than a meteoric origin, and that it re- 

 sults from the motion of meteors which fall into the sun an idea first put 

 forth by Mr. "Waterson at the meeting of the British Association at Hull 

 Whatever may be the value of this hypothesis, we would ask whether it 

 would not be more simple to admit that the solar heat proceeds simply from 

 the rotatory movement of the sun. Mr. Thomson admits himself that the 

 rotation is necessary to the production of the heat. It is known that the sun 

 moves on its axis, and what use is this invention of meteorites, which nothing 

 justifies ? This idea of deriving heat from motion, which was rejected more 

 than thirty years ago, suggests the hypothesis which assigns an analogous 

 origin to terrestrial, and hence to planetary magnetism. The question of 

 solar magnetism has been conclusively settled by the researches of M. Secchi, 

 director of the observatory at Rome. The sun, which is a source of light, 

 and a source of heat, is then a source of magnetism also heat, light, electric- 

 ity, and magnetism have then a common origin matter in motion. M. 

 Nickles, Paris Correspondence Silliniaris Journal 



FARADAY OX THE XATUEE OF GRAVITY AXD PHYSICAL FORCE. 



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It is probably of great importance that our thoughts should be stirred up at 

 this time to the reconsideration of the general nature of physical force, and 

 especially to those forms of it which are concerned in actions at a distance. 

 These are connected very intimately with those which occur at insensible dis- 

 tances ; and it is to be expected that the progress which physical science has 

 made in later times will enable us to approach this deep and difficult subject 

 with far more advantage than any possessed by philosophers at former pe- 

 riods. At present we are accustomed to admit action at sensible distances, 

 as of one mag-net upon another, or of the sun upon the earth, as if such ad- 

 mission were itself a perfect answer to any inquiry into the nature of the 

 physical means which cause different bodies to affect each other ; and the 

 man who hesitates to admit the sufficiency of the answer, or of the assumption 

 on which it rests, runs some risk of appearing ridiculous and ignorant before 

 the world of science. Yet Newton, who did more than any other man in 

 demonstrating the law of action of distant bodies, including among such the 

 sun and Saturn, which are nine hundred millions of miles apart, did not leave 

 the subject without recording his well-considered judgment, that the mere at- 

 traction of different portions of matter was not a sufficient or satisfactory 

 thought for the philosopher. That gravity should be innate, inherent, and es- 

 sential to matter, so that one body may act upon another at a distance through 

 a vacuum without the mediation of any thing else, by and through which their 

 action and force may be conveyed from one to another, is, he says, to him a 

 great absurdity. Gravity must be caused by an agent acting constantly ac- 



