558 Mr. L. Sehwendler on a Method of using 



The continuous broken line joins together my six points of 

 observation. The dotted line is Matthiessen's curve of con- 

 ductivity on the same scale, viz. absolute measure, with some 

 of his points of observation marked on it ; but no alloys be- 

 tween somewhere about E and A seem to have been actually 

 examined by him. 



The position of pure copper (from Matthiessen's measure- 

 ment) cannot be shown in the diagram : the conductivity 

 decreases at such a tremendous rate with the slightest per- 

 centage of tin that the ordinate for pure copper is 600 scale- 

 divisions, whereas the greatest height shown in the diagram, 

 that of the point B, is only about 90. 



It is unnecessary to call attention to the extraordinary be- 

 haviour of the alloy C containing 31*7 per cent, of tin (that 

 is, the alloy SnCu 4 ), or to point out how easily it might have 

 been supposed to be a distinct metal. 



LXVI. On a Simple Method of using an insignificant Fraction 

 of the main Current produced by a Dynamo-electric Machine, 

 for Telegraph-purposes. By Louis Schwendler*. 



THE currents which a dynamo-electric machine is capable 

 of generating through a small external resistance are 

 enormously strong, sufficiently constant, and exceedingly 

 cheap ; I always thought, therefore, it would be of technical 

 as well as of economical importance to use them for signalling- 

 purposes. 



The only difficulty was how to solve the problem practically. 

 Manifestly the currents could not be produced through the 

 telegraph-lines, in the ordinary manner of applying dynamo- 

 electric machines ; for, in the first place, telegraph-lines offer 

 high resistances, and, in the second place, the use of the closed- 

 circuit system would become imperative. However, some time 

 ago a very simple method occurred to me, which appears to 

 contain the germs of practical success ; and having made of 

 late some experiments on the subject, I do not hesitate to com- 

 municate the result. 



Suppose we have a dynamo-electric machine, the two ter- 

 minals of which are connected by a resistance r through which 

 any kind of useful work is to be performed by the current. 

 For instance, during night r may consist of an electric arc, and 

 the useful work done by the current is given out as light for the 

 signalling-office ; or during daytime r may consist of another 



* Communicated by the Author. 



