218 ANNUAL OP SCIENTIFIC DISCOVERY. 



ion between light and magnetism. What wonder, then, if this unify- 

 ing instinct, this yearning to find the mystic bond which unites these 

 forces, this prediction of the human mind that all the forces of nature 

 are but branches of a common root, what wonder, I say, if it jumped 

 its bounds and cried"! have it! "too soon? For a long time the 

 optic axis, and it alone, was chargeable with these phenomena, phe- 

 nomena which it was now hoped there would be little difficulty in re- 

 ferring to their proper cause, and regarding as examples of the modi- 

 cation of force by the peculiarities of aggregation. 



The lecturer then pointed out the bearing of the described results 

 upon the problem of the diurnal range of the magnetic needle. Pro- 

 fessor Faraday had referred the matter to the modification of atmos- 

 pheric magnetism by the sun's rays. That an effect was produced 

 here could not for a moment be doubted, but the precise extent of 

 this effect was still an open question. The discovery of a decimal 

 period by Lament threw a great difficulty in the way of any theory 

 which would refer the diurnal range to thermic action ; and the diffi- 

 culty was greatly increased by the observation of Col. Sabine, who 

 connected Lament's discovery with that of Schwabe regarding the 

 solar spots. But whatever the result of future inquiries as to the 

 direct magnetism of the sun may be, no theory which proposes to ex- 

 haust the subject can afford to omit the mediate operation of the sun 

 by his heat ; not however confining it to the atmosphere, but extend- 

 ing it also to the earth's solid crust. Let us look once more to our 

 experiments. The line of greatest density is that of strongest mag- 

 netic power. The body operated upon by the magnet is itself a mag- 

 net, and it is an experimental fact that it is a stronger magnet along 

 the line of greater density than along any other line. If instead of 

 increasing the density in one direction we increase it in all direc- 

 tions, we thereby augment the general magnetic power of the body. 

 Anything, therefore, which tends to increase density increases mag- 

 netic power ; and whatever diminishes density diminishes magnetic 

 power also. Knowing this, the conclusion is inevitable, that the local 

 action of the sun upon the earth's crust must influence, in some de- 

 gree, the resultant effect. The action here meant is wholly different 

 from that hitherto speculated on, and which had reference to the gen- 

 eration of thermo-electric currents which affect the needle. The sim- 

 ple mechanical change of density is what is meant. It is a true cause, 

 and no complete theory can omit taking it into account. 



DETERMINATION OF VELOCITIES.* 



The invaluable instrument which we call a pendulum, has been ap- 

 plied to an infinity of objects, and always with characteristic advan- 

 tages in point of precision or sensibility. It was only recently that by 



translated from the Mechanics Magazine, from M. De Boucheporn's paper, read 

 before the French Academy of Sciences. 



