il _ JOH*H 

 } — \ ZnO. 



Royal Society. 541 



Finally, zincethyle is decomposed by water into oxide of zinc and 

 hydride of ethyle — 



OH 5 Zn" 

 HO 



It is also similarly acted upon by the hydrated acids and by the hy- 

 drogen compounds of chlorine, bromine, iodine, fluorine and sulphur. 



The behaviour of zincethyle in contact with the electro-negative 

 elements is highly remarkable, and cannot fail to have an important 

 influence upon our views of the condition of bodies at the moment of 

 chemical change, — a subject so ably discussed by Brodie*, whose in- 

 genious views I consider to receive a new support in these reactions 

 of zincethyle, by the singular way in which ethyle, a body low down 

 in the electro-positive series, unites with oxygen, chlorine, &c, in 

 the presence of a large excess of the intensely electro-positive zinc- 

 ethyle. This behaviour also strikingly confirms the suggestions I 

 ventured to make in my former memoirf, relative to the moleculo- 

 symmetrical form of organo-metallic compounds. In the inorganic 

 combinations of zinc, this metal unites with one atom only of other 

 elements ; a very unstable peroxide, not hitherto isolated, being the 

 only exception. The atom of zinc appears, therefore, to have only 

 one point of attraction, and hence, notwithstanding the intense 

 affinities of its compound with ethyle, any union with a second body 

 is necessarily attended by the expulsion of the ethyle. 



" Note on the Magnetic Medium." By Prof. A. W. Williamson. 



In a letter to Mr. Faraday recently published in the Philosophical 

 Magazine, Dr. Tyndall brings forward some important considera- 

 tions on the subject of magnetic philosophy. 



It has been known for some time that the phenomena of dia- 

 magnetism may be produced artificially in bodies which are usually 

 considered magnetic. For this purpose it is only necessary to 

 plunge the magnetic body into a yielding medium more magnetic 

 than itself. When thus exposed to the action of a magnet it recedes 

 from the poles, because the volume of the medium which it dis- 

 places is more powerfully attracted. 



This fact naturally suggested the idea, that all repulsion by the 

 magnet might be owing to the attraction exercised on the medium 

 being stronger than that on the body repelled ; — just as balloons are 

 driven upwards by the superior weight of the displaced volume of 

 air. And as phsenomena of diamagnetism are observed in a so-called 

 vacuum, it was thought that some "magnetic medium" might be 

 present there. 



I do not purpose on this occasion to enter upon the general 

 question of the evidence which may be adduced for or against this 

 important conclusion ; for it could only be proved satisfactorily by 

 considerations including phenomena of the most varied kind, such 

 as electricity, light, chemical action, &c, to which it must neces- 

 sarily apply. But it might be disproved by any one well-understood 

 fact contradictory to it. 



Now it appears to me, that the facts adduced by Dr. Tyndall are 



* Philosophical Transactions, 1850, p. 789. f Ibid. 1852, p. 438. 



