NATURAL PHILOSOPHY 189 



Some are much surprised that I should, as they think, venture to oppose 

 the conclusions of Newton ; but here there is a mistake. I do not oppose 

 Newton on any point ; it is rather those who sustain the idea of action at a 

 distance, that contradict him. Doubtful as I ought to be of myself, I am 

 certainly very glad to feel that my convictions arc in accordance with his 

 conclusions. At the same time, those who occupy themselves with such 

 matters ought not to depend altogether upon authority, but should find 

 reason within themselves, after careful thought and consideration, to use and 

 abide by their own judgment. Newton himself, whilst referring to those 

 who were judging his views, speaks of such as are competent to form an opin- 

 ion in such matters, and makes a strong distinction between them and those 

 who were incompetent for the case. 



But after all, the principle of the conservation of force may by some be 

 denied. Well, then, if it be unfounded even in its application to the small- 

 est part of the science of force, the proof must be within our reach, for all 

 physical science is so. In that case, discoveries as large or larger than any 

 yet made, may be anticipated. I do not resist the search for them, for no 

 one can do harm, but only good, who works with an earnest and truthful 

 spirit in such a direction. But let us not admit the destruction or creation 

 of force without clear and constant proof. Just as the chemist owes all the 

 perfection of his science to his dependence on the certainty of gravitation ap- 

 plied by the balance, so may the physical philosopher expect to find the 

 greatest security and the utmost aid in the principle of the conservation of 

 force. All that we have that is good and safe, as the steam-engine, the elec- 

 tric-telegraph, c , witness to that principle, it would require a perpetual 

 motion, a fire without heat, heat without a source, action without reaction, 

 cause with effect, or effect without a cause, to displace it from its rank as a 

 law of nature. 



MOXOGEXESIS OF FORCE. 



A lecture which has attracted considerable attention has been delivered 

 before the Royal Institution London during the past year, by Mr. Alfred 

 Smce, on the " Monogenesis of the Physical Forces." The conclusion to 

 which Mr. Smee arrives is, that " attraction acting on attracted matter is the 

 source of all force, and that, therefore, every physical force has a monogene- 

 tic orgin, and when generated, a truly equivalent power." 



DENSITY OF THE EARTH. 



The experiments of the English Astronomers in the Harton Coal Pit, ac- 

 cording to Rev. S. Haughton, (Phil. Mag. [4], xii. 50), give for the mean 

 density of the earth, 5'480. The pit was 1260 feet deep, and the seconds 

 pendulum gained two and a quarter seconds per day at the bottom of the 

 coal pit. 



But the calculations of Mr. Airy, the Astronomer Royal (ib, p. 231) as 

 given in the same journal vol. xii. p. 231, arrive at 6-566 as the mean den- 

 sity, which number at page 468 is changed to 6-809 6-623, the variation 

 depending on the relative value of some of the observations. 



