i873«] Actinism and Magnetism. 299 



been brought before the public in rather a piecemeal sort of 

 way, it may not be deemed amiss that they should be here 

 presented in a more regular and condensed form. 



The duality observed in all electrical and magnetical phe- 

 nomena, whether paramagnetic or diamagnetic, raises a 

 strong presumption that there is in nature a somewhat to 

 which this dualism is due. The remarkable circumstance 

 that the magnetic influence, with its duality of manifestation, 

 passes through the free ether, renders almost compulsory 

 the inference that it is in this subtle medium that the 

 origin of the dualism is to be sought. It is well known that 

 there is a remarkable connection between the earth's mag- 

 netism and the solar spots, and that all magnetic obser- 

 vatories in our globe have been affected by certain sudden 

 luminous flashes which have been observed in the solar 

 photosphere. There can, therefore, be no doubt of the fact 

 that the magnetic influence does pass through the free 

 ether, and that magnetic dualism is thus wafted onwards 

 like luminous waves through the ethereal expanse. Now it 

 is almost inconceivable that this should happen unless there 

 were some intrinsic dualism in the ether itself — unless, in 

 short, it were composed of two fluids, which, like the 

 nitrogen and oxygen gases of our atmosphere, are mechan- 

 ically alike, but chemically different. It is needful to sup- 

 pose them to be mechanically alike — both perfectly elastic 

 fluids, and that, on their particles being set a vibrating, 

 they vibrate in the same times, and that these vibrations 

 are wafted onwards in similar waves 0? definite lengths. 

 At least, there have not yet been distinguished any pheno- 

 mena from which it could be inferred that the supposed two 

 fluids differ from each other in their mechanical constitution 

 in any appreciable degree. But it is equally needful to 

 suppose these two fluids to differ from each other in their 

 relations to the molecules, ultimates, and atoms of bodies 

 endowed with the energy of gravitation, of which the ethereal 

 fluids are themselves destitute ; for it is only by such dif- 

 ferences that the existence of two ethereal fluids can be 

 established. 



Waiving for the present the question of the relation of 

 the duality of the ether to that of magnetism, and regarding 

 meanwhile the former as merely a convenient assumption, 

 let us, by means of it, endeavour to explain actinic action 

 in the case of iodide of silver, and in particular to account 

 for the formation of the latent image, and its subsequent 

 development. 



Let it be granted that each molecule of the iodide of 



