V ^ 



L 179 J 



XVI. Indices of Refraction for Electric Waves, Measured by 

 a Modified' Radio-Micrometer. By George Pierce*. 



HHIIE Receiving Instrument. — In a previous paper f the 

 writer has described a modified form o£ radio-micrometer, 

 adapted to the quantitative detection of short electric 

 waves. The instrument there described is similar to the 

 radio-micrometer of Professor Boys, except that the simple 

 thermal couple of the Boys suspension is replaced by a 

 thermal-junction combined with a small electric oscillator, 

 like that of KlemencicJ. Klemencic's device is shown in 

 fig. 1. y\t consists of two sheets of brass, M, 10 centim. 

 broad and 30 centim. long, placed 3 centim. apart, and having 



Fi<r. 1 . 



P 



M 



X 



M 



J 



soldered to them respectively a very fine platinum and a 

 very fine platinum- nickel wire, which are crossed at K, and 

 are thence conveyed off at right angles and soldered at their 

 other ends to the leads, I, of a sensitive galvanometer. 

 Electric oscillations between M and M produce heating at 

 the knot, K, which gives rise to a thermo-electromotive force 

 at the knot, and, consequently, to a current through the 

 galvanometer. t 



In the form of detector used in the present experiment, a 

 similar, but much smaller, resonating thermal-junction is 

 employed ; but, instead of communicating with a separate 



and Physikalische Zeit- 



4 | 





* Communicated by the Author. 

 t Pierce, Am. Journ. of Sci. ix. p. 25 

 schrift, i. p. 46 (18 Aug. 1900). 



\ KleinencicJ Wied. Ann. xlv. p. 62 (1892 



