On the Existence of a Magnetic Medium in Space. 205 



In the February Number (p. 133), I have adduced an argument 

 to prove, on the assumption of the illegitimacy of starting from 

 a fixed ellipse, that the apsidal equation contains the disturbing 

 force as a factor. It is now shown that the illegitimacy of that 

 procedure cannot be assumed on the ground of its giving rise to 

 non-periodic factors in the development of the radius-vector. 

 I shall take a future occasion for showing that the argument, 

 together with the new theorem respecting the eccentricity of 

 the moon's orbit, which depends upon it, may still be main- 

 tained. 



Cambridge Observatory, 

 Feb. 16, 1855. 



XXIX. On the Existence of a Magnetic Medium in Space. 

 By John Tyndall, Ph.D., F.R.S. 



My dear Mr. Faraday, 



FEW, I imagine, who read your memoir in the last Number 

 of the Philosophical Magazine, will escape the necessity 

 of reconsidering their views of magnetic action. We are so 

 accustomed to regard the phenomena of this portion of science 

 through the imagery with which hypothesis has invested them, 

 that it is extremely difficult to detach symbols from facts, and 

 to view the latter in their purity. This duty, however, is now 

 forced upon us; for the more we reflect upon the results of 

 recent scientific research, the more deeply must we be convinced 

 of the impossibility of reconciling these results with our present 

 theories *. In the downfall of hypotheses thus pending, the 

 great question of a universal magnetic medium has presented 

 itself to your mind. Your researches incline you to believe in 

 the existence of such a medium, and lead you, at the same time, 

 to infer the perfect identity of magnetism and diamagnetism. 



In support and illustration of your views, you appeal to the 

 following beautiful experiments : — Three solutions of proto- 

 sulphate of iron are taken ; the first, I, contains 4 grains ; the 

 second, m, 8 grains; and the third, n, 16 grains of the salt to a 

 cubic inch of water. Enclosed in hollow globules of glass, all 

 these solutions, when suspended in the air before the pole of a 

 magnet, are attracted by the pole. You then place a quantity 

 of the medium solution, m, in a proper vessel, immerse in it the 

 globule containing the strong solution n, and find that the 

 latter is still attracted; but that when the globule containing 

 the solution / is immersed, the latter is repelled by the mag- 



* Some of tin' reason* which induce the writer to hold this opinion are 

 given in the Uukeriau. Lecture of the Royal Society for the present year. 



