76 Intelligence and Miscellaneous Articles. 



At present the writer does not venture to put forth any definite 

 theory respecting the presence and nature of the nuclei which are so 

 universally diffused throughout the atmosphere ; but when it is con- 

 sidered how much sodic chloride is constantly present in the air, and 

 what quantities of sulphurous acid are evolved daily, which becomes 

 partly converted into sulphuric acid, the presence of particles of sodic 

 sulphate in the air would not be surprising ; and that it does exist is 

 proved by drawing air through water and finding comparatively large 

 quantities in the solid matter arrested by water. 



Sodic sulphate solutions, too, crystallize on exposure much more 

 readily than those of any other salt. The other salts which form 

 supersaturated solutions are certainly less diffused than sodic sulphate. 



IX. Intelligence and Miscellaneous Articles, 



ON THE DISTRIBUTION OF MAGNETISM. BY M. JAMIN. 



AT the last Meeting of the Academy, M. Treve communicated a 

 note on magnetism, in which he states, among other things, that 

 the poles of a magnet are displaced, being removed from the extre- 

 mities, when an armature of soft iron is applied. He believes he 

 demonstrates this by placing opposite to the magnet a magnetized 

 needle, by showing that its direction changes after the application 

 of the contact, and by supposing that the pole is in the prolonged 

 direction of the needle. 



We ought first to define the word pole ; we must then remark 

 that, in this experiment, the magnetized needle is submitted to the 

 attractive action of the steel which forms the magnet, of the iron 

 which constitutes the contact, and, again, to the attraction or re- 

 pulsion of the free magnetism of the magnet. Its direction is along 

 the resultant of these actions — a resultant evidently very compli- 

 cated, depending on the distance, the weight, and the form of the 

 contact : it is clear that the direction of this resultant cannot lead 

 to any precise conclusion. 



What it is necessary to determine here is the distribution of the 

 magnetism in the magnet, both before and after the application of 

 the contact ; this is a question with which I have long occupied 

 myself, and on which I will now say a few words. 



I study this distribution by two mutually corroborative processes. 

 The first consists in placing upon a point of the magnet a small 

 electromagnet of soft iron enveloped in copper wire w T hich commu- 

 nicates with a galvanometer, and suddenly pulling it away. An 

 induction-current is produced, a galvanometric deflection ; and from 

 the magnitude of the arc of impulsion I can calculate, after a suit- 

 able graduation, the magnetic intensity at the point touched. 



The second process, analogous to Coulomb's, consists in placing on 

 the point one wishes to study a small sphere of soft iron supported 

 by a spring, which is stretched progressively till separation takes 

 place. Its tension at that moment is proportional to the square of 

 the magnetism at the point of contact. 



