356 Messrs. Wanklyn and Cooper on the 



Considering that the resistance varies as the absolute tem- 

 perature of the conductor, according to a law first expressed 

 by Helmholtz, the value of E may be put for B/ for small 

 variations of temperature ; and as during an interval of con- 

 stant current the heat generated and that radiated off will be 

 equal, we obtain 



<T'-T)|, .-. Q'=^/(Z^)8 . . . (1) 



in which T' — T represents the movement of the pencil, and S 

 is constant. 



For any other temperature T", 



C /2 : 



V 



'(T" -T)S 

 R V 



For small differences of C" and C, 



(C"-C') 2 =2C"(C"-C); 

 that is to say, small variations of current will be proportional 

 to the variations in the temperature of the strip. 



To determine the value of a diagram in Weber's or other 

 units of current, it is only necessary, if the variations are not 

 excessive, to average the ordinates, and to determine their 

 value by equation (1), or from a Table. 



These observations may suffice to show the possibility of 

 regulating and measuring electric currents with an ease and 

 certainty quite equal to that obtained in dealing with currents 

 of liquids such as gas or water ; and the time may not be far 

 distant when the use of such an instrument will also become 

 a public necessity. 



Other forms of the instrument will readily suggest them- 

 selves to the mind of the constructive engineer ; but the two 

 typical forms I have described on this occasion will suffice, 

 I think, to show its general character. 



LVII. Products of the Oxidation of Wool. Cyano-propionic* 

 Acid. By J. Alfred Wanklyn and W. J. Cooper |- 



IN the course of the investigations which have led up to 

 the moist-combustion process, we have come across some 

 results which appear to be worth recording. On the present 

 occasion we single out the oxidation of wool, so as to produce 

 large quantities of a new nitrogenous acid endowed with great 

 stability. 



When wool, dissolved in water by the aid of about three 



* Apparently, judging from the reaction with potash, the acid is iso- 

 cyano-propionic acid. — J. A. W. 

 t Communicated by the Authors. 



