Intelligence and Miscellaneous Articles. 327 



and which are so abundant in the light of electric discharges ; and 

 I found it to be so. A drop of disulphate of quinine on a porcelain 

 tablet seemed like a luminous patch on a faint ground ; and crystals 

 of platinocyanide of potassium were so bright, that the label on the 

 tube which contained them (and which by lamplight could not be 

 distinguished from the salt at a little distance) seemed almost black 



by contrast. i • ^ v * 



These eflFects were so strong in relation to the actual mtensity ot 

 the lio-ht, that they appear to aiford an additional evidence of the 

 electri'c origin of this phenomenon, and as such I hope they may 

 interest some of your readers. 



NOTE ON THE TANGENT-GALVANOMETER. 

 BY G. JOHNSTONE STONEY. 



To the Editors of the Philosophical Magazine and Journal. 



Queen's University, Dublin Castle, 

 Gentlemen, March 15, 1858. _ 



My friend Dr. Robinson of Armagh has been so good as to point 

 out to me the fact, that a modification of Gaugain's rheometer 

 has been suggested by Jacobi which combines the advantage of M. 

 Gauo-ain's arrangement with a freedom from liability to those errors 

 of which I sought to determine the laws in a paper on the adjust- 

 ments of the tangent-galvancmeter published in last February's 

 Number of the Philosophical Magazine. As Jacobi does not seem 

 to have contemplated this advantage in the form which he gave 

 to the instrument, it may be useful to direct the attention of phy- 

 sicists to its existence. 



Gaugain's rheometer, as modified by Jacobi, consists of two equal 

 current circles having a common axis, along which they are sepa- 

 rated by an interval equal to the radius of either. The needle is 

 swung midway between them, and the circles are to be traversed m 

 the same direction by currents of equal intensity. 

 I am, Gentlemen, 



Yours faithfully, 



G. Johnstone Stoney. 



ON THE DAILY FALL OF THE 15AR0METER AT TORONTO. 

 BY THOMAS HOPKINS, ESQ. 



In this paper the author endeavours to show that the vapour, which 

 in tlie early part of the day was produced by solar heat at the surface, 

 by its expansive power, bore that heat to the upi)er regions of the 

 air, where it was condensed by the cold of the gases in that situation, 

 when the heat of elasticity was set at liberty to warm and expand 

 the ga.ses, and that it was this expansion which reduced atniospiicnc 

 pressure in tlie locality and caused a fall of the barometer.— Proc. 

 Rofj. Sac. Feb. I, IHJH. 



