218 Mr. A. B. Northcote on Parathionic Acid. 



liquid dielectric the currents produced depend for their force 

 upon the amount of electricity sent in and its tension, and for 

 their direction upon the position of the two conducting wires, 

 the one that brings the charge and the other that conveys it 

 away. The density of the medium will render the momentum 

 of the particles so much greater in turpentine than in air in the 

 proportion of their respective specific" gravities. Hence a point, 

 or a system of points free to move in the liquid dielectric, will 

 not so much determine the direction of the current as be itself 

 determined by that direction. It is in fact helpless in so dense 

 a medium. It is swept round by the current, and moves points 

 forwards or points backwards with the current. 



If this be the true state of the case (and my experiments lead 

 me to no other conclusion), the theory of the fly requires a dif- 

 ferent expression for an aerial, as compared with a liquid dielec- 

 tric; its behaviour is also different in air of different densities, 

 and also when wholly or partially enclosed, — also when the 

 points are covered ; and even then there is a different action in 

 the presence of flame. In short, there is no one expression that 

 fairly represents the electric fly. It modifies its behaviour 

 according to circumstances; and, like a good subject, has no 

 law of its own, but conforms to the laws of the community of 

 which it is a member. 



King's College, London, 

 January 1864. 



XXXVIII. On Parathionic Acid. By Augustus Beauchamp 

 Northcote, B.A. } F.C.S., Lecturer on Chemistry in Exeter 

 College, Oxford*. 



SINCE the days of Sertiirnert, who in 1819 announced that 

 in the residues from the preparation of ether he had dis- 

 covered three acids related to each other, and composed of alcohol 

 and sulphuric acid, the opinion that there exist certain modifica- 

 tions of the sulphovinic acids has been gaining ground, until of 

 late years it has become a matter of certainty. Placing isethionic 

 acid apart, the experiments of Gerhardt and Berthelot on the 

 sulphethylic compounds, and of Church on the sulphomethylic, 

 have shown that side by side with the sulphovinic acids, and pro-, 

 duced by processes which should have yielded the ordinary 

 varieties of those acids, there stand compounds possessing suffi- 

 ciently well-marked characteristics to allow of their ranking as 

 isomeric modifications. 



The whole question of isomerism has recently assumed pecu- 



* Communicated by the Author. 



t Gmelin (Cav.*Soc.), vol. viii. p. 415. 



