On the Measurement of the Intensity of Electric Currents. 529 



After the supposition, that the change in colour arose from 

 the presence of a foreign substance, had thus been confirmed, I 

 found that in so narrow a tube even the smallest quantity of 

 fatty matter on the negative wire was sufficient to make the 

 light white. Mere contact with the fingers is often sufficient for 

 this purpose; and, indeed, not only by the employment of wires 

 of aluminium, but likewise of copper, brass, platinum, and pro- 

 bably every other metal which is not volatile at the temperature 

 in question, the same results are obtained. On the positive wire 

 fat produces little or no effect ; it may either be placed on its 

 point, or at some distance from it. 



Tallow, fatty oils, stearic acid, and wax behave all in a similar 

 way. "When we place some of either of the above on the nega- 

 tive wire, the greasy part appears red at first, whilst the rest of 

 the wire shines with blue light. Immediately afterwards the 

 spot is surrounded with a mantle of reddish light which gradu- 

 ally disappears. The blue light on the rest of the wire simul- 

 taneously turns white, and the red light between the two wires 

 likewise changes to brown and white. It is probable that the 

 fat was decomposed, but through the quantity being so small 

 the decomposition could not be proved. 



LXVIII. On the Measurement of the Intensity of Electric Currents 

 by means of a Tangent-galvanometer or a Multiplier. By Ch. 

 V. Zenger, Professor of Physics, and Member of the Physical 

 Institute*. 



MR. G. JOHNSTONE STONEY published in this Journal 

 (February 1858) a formula of correction for the length 

 of the needle and for the derangement of its point of suspension. 

 Mr. Stoney in his paper has mentioned the researches of MM. 

 Gaugain and Bosscha, but he does not notice my researches on 

 the corrections to be applied to tangent-galvanometers and to 

 multipliers, although I published them three years agof, and 

 although they were discussed in Liebig and Kopp's Jahresbericht. 

 Mr. Johnstone Stoney examines two cases, viz. that of a common 

 galvanometer, and that of Gaugain's arrangement ; he found in 

 the first case the formula of correction, 



;=Ktau0£l+^\ 2 sin 2 <A 



K being a constant so long as the same needle is used, 0= the 



* Communicated by the Author. 



f Proceedings of the Imperial Academy of Vienna, vol. xvii. April 19; 

 and vol. xviii. November 2, 1855. 



