322 Royal Institution. 



The general scope of the argument from the negation of per- 

 petual motion leads the mind to regard the so-caUed imponderables 

 as modes of motion, and not as different kinds or species of matter ; 

 the recent progress of science is continually tending to get rid of the 

 hjTJOtheses of fluids, of occult qualities, or latent entities, which 

 might have been necessary in an earlier stage of scientific inquiry, 

 and from which it is now extremely difficult to emancipate the 

 mind : but if we can, as it is to be hoped we shall, ultimately arrive 

 at a general dynamic theory, by which the known laws of motion 

 of masses can be applied to molecules, or the minute structural 

 pEirts of matter, it seems scarcely conceivable that the mind of 

 man can further simplify the means of comprehending natural 

 phsenomena. 



February 22, 1856. — "On certain Magnetic Actions and Affec- 

 tions." By Michael Faraday, D.C.L., F.R.S. 



All bodies subject to magnetic induction, when placed in the 

 ordinary magnetic field between the poles of a magnet, are affected; 

 paramagnetic bodies tend to pass bodily from weaker to stronger 

 places of force, and diamagnetic bodies from stronger to weaker 

 places of force. If the bodies are elongated, then those that 

 are paramagnetic set along the lines of force, and those that are 

 diamagnetic across them : but if these bodies have a spherical 

 form, are amorphous, and are perfectly free from permanent mag- 

 netic charge, they have no tendency to set in a particular direction. 

 Nevertheless, there are bodies of both classes, which being crystal- 

 line, have the power of setting when a single crystal is wrought into 

 the form of a sphere, and these are called magnecrystals ; their 

 number is increasing continually ; carbonate of lime, bismuth, 

 tourmaline, &c., are of this nature. Bodies which being magnetic, 

 set, because they are elongated, are greatly influenced in the force of 

 the set by the nature of the medium surrounding them, and to such 

 an extent that they not merely vary in their force from the maximum 

 to nothing, but will often set axially in one medium, and equatori- 

 ally in another. Yet the same bodies, if magnecrystallic and 

 formed into spheres, though they set well in the magnetic field, will 

 set with the same force whatever the change in the media about 

 them, and are perfectly freed from the influence of the latter. 

 Thus, if a crystal of bismuth formed into a sphere, or a vertical cylin- 

 der, has, when suspended, its magnecrystallic axis horizontal, and 

 if the various media about it, from saturated solution of sulphate 

 of iron, up to phosphorus, through air, water, alcohol, oil, be 

 changed one for another, no alteration in the amount of torsion 

 force required to displace the magnecrystal will occur, provided 

 the force of the magnet be constant, notwithstanding that the list 

 of media includes highly paramagnetic and diamagnetic bodies ; and 

 in such cases the measurement of the power of set is relieved from 

 a multitude of interfering circumstances existing in other cases, and 

 that power which is dependent upon the internal structure and con- 

 dition of the substance is proved to be, at the same temperature, 

 always the same. 



