1865.] 257 [Cha?e. 



of the axis of rotating bodies to parallelism with the earth's axis.* 

 (Math. Monthly, i, 307 ; ii, 95, 380, 882.) The rationale is gene- 

 rally so obvious that the necessity of the experiments may reasonably 

 enough be doubted by some, while others may question the validity 

 of any inferences as to magnetic motions that are drawn from the 

 eflfect of impulses which arc confessedly purely mechanical. 



Such doubts may perhaps be removed by considering, 1st, the well- 

 known danger of being led astray by the simplest undetected fallacy 

 in d priori reasoning, which renders it desirable to obtain experi- 

 mental verifications of every philosophical inference ; 2d, that if all 

 forms of force are, as is so generally supposed, mutually convertible, 

 the convertibility can only be discovered through their mechanical 

 momentum ; and 3d, that all the experiments illustrate the maynetic 

 mjluence of a fluid controlled hy the reaction of distvrhed (jravita- 

 tion. I have shown that forces proceeding in lines corresponding to 

 those which represent solar and planetaryf influence, produce mag- 

 netic deflections equivalent to the observed solar-diurnal, annual, de- 

 cennial, and secular variations; and if it can be also shown that 

 gravitation is an adequate force, we need seek no farther for a vera 

 causa, or for conclusive evidence of the correlation of all the great 

 cosmical forces. 



Whatever theory we may favor respecting the nature of force, and 

 the manner or medium of its transmission, — whether we consider 

 with Fresnel and Grove, that the luminiferous and kinetic aether is 

 material and ponderable ; with Mossotti and Faraday, that it is im- 

 ponderable ; or with Dana, that the hypothesis of any medium is en- 

 tirely supererogatory if (Amer. Jour, of Science [2], iv, 379, 382), 

 it will be generally admitted that the quantity of motion is the 

 proper measure of force. In an ordinary tempest, every flash of 

 lightning is followed by a thunder-clap, which is occasioned by the 



* Mr. Ferrel refers, for a beautiful illustration of some of his propositions, to 

 Foucault's experiments with the gyroscope. (Amer. Jour, of Science [2], xv, 263 ; 

 xix, 141.) 



f The connection which has been pointed out by Sabine between Schwabe's 

 theoretic course of the solar-spot phenomenon and the magnetic 10-11-year pe- 

 riod (Phil. Trans., 1852, Art. VIII), acquires a new interest from Prof. Wolfs 

 continued investigations into the influence of the several planets upon the sun- 

 spot curve. (See Monthly Notices of the Royal Ast. Soc, May 12, 1865.) 



J Is the " pulsating 7>iolecular force''' of Prof. Dana's hypothesis material or 

 immaterial? If the latter, is it intelligent or unintelligent? IIow can momen- 

 tum be imparted by velocity without material mass, unless it be by the direct 

 and voluntary act of a competent intelligence ' 



