72 hitelligence and Miscellaneous Articles, 



sional changes of the height of the barometer, and on their con- 

 nexion with the changes of temperature arising from the seasons 

 and from the condensation of aqueous vapour. 



A meeting of this Society was 'also held on Monday evening, 

 May 16th, Dr. Thackeray, V.P., in the chair. A letter from A. De 

 Morgan, Esq., to the Rev. George Peacock, was read, containing 

 a sketch of a method of introducing discontinuous constants into 

 the arithmetical expressions for infinite series. Also a memoir by 

 P. Kelland, Esq., of Queen's College, on the mathematical results 

 of a mixture of elastic fluids (as air and vapour in the atmosphere), 

 and on the theory of heat. With regard to the latter subject, the 

 object was to show that there is a translation backwards or forwards 

 of the calorific particles, consequent on and varying in intensity 

 with the transverse vibration. Mr. Hopkins made some statements 

 respecting experiments recently made on the temperature of mines 

 and the doctrine of central heat. Mr. Airy gave an account of ob- 

 servations of temperature made during the great solar eclipse of 

 May 15th. 



XV. Intelligence and Miscellaneous Articles. 



ON THE FEEBLE ATTRACTION OI? THE ELECTRO-MAGNET FOR 

 SMALL PARTICLES OF IRON AT SHORT DISTANCES. 



To the Editors of the Philosophical Magaziiie and Journal. 

 Gentlemen, 



THE enormous sustaining power of the electro-magnet has for 

 some time been exhibited as a matter of great curiosity, but 

 its very feeble attraction for small particles of iron at short distances 

 is not, I believe, very generallyknown. This fact was first mentioned 

 to me by Mr. Clarke, magnetical instrument-maker, which since 

 then I have frequently noticed myself. I am not aware that any 

 explanation of this seeming anomaly has as yet been given ; I have 

 therefore ventured to oSer one, which, if considered satisfactory, 

 and of interest sufficient to deserve a place in your valuable Journal, 

 I shall be obliged by its insertion. 



It will be necessary first to observe the phsenomena which take 

 place when a piece of soft iron is under the influence of the 

 ordinary horseshoe magnet. When the arma- 

 ture 5' ?«' is brought near to the magnet NS, > n. 



magnetism is induced in 5' n'; and according to f/^~^^\\ 

 the law of magnetic induction each extremity 

 of s' n' has its state of polarity opposite to that 

 of the adjacent pole of the magnet N S, and a 

 tendency to approach each other immediately n Jl Up- 



takes place, and if the force of attraction be gi i^ ~\ „» 



sufficient to overcome the inertia of s'n', con- 

 tact will instantly follow. 



If the armature be sufficiently massive to receive all the mag- 



