428 



THERMO-ELECTRIC MEASUREMENT OF HEAT. 



ffl 



Fig. 168. 

 Scheme of thermo-electric arrangements for estimating the temperature. 



B. Thermo-electric Method. This method enables us to determine the 

 temperature accurately and rapidly (Fig. 168, 1). The thermo-electric galvanometer 

 of MeissnerYand \ Meyerstein consists of a circular magnet (TO), suspended by a 

 thread of silk (c), to'^which a small mirror (S) is attached. A large stationary 

 bar magnet (M) is placed near the magnet (m), so that the north poles (n and N) 

 of both magnets point in the same direction, and it is so arranged that the sus- 

 pended magnet is caused to point to the north by a minimal action of M. 



A thick copper wire (b, b) is coiled several times round m (although in the Fig. 

 it is represented as a single coil), and the ends of the wire are soldered to two 

 thermo-elements, r each composed of two different metals iron and German silver, 

 the two similar free elements being united by a wire (61), so that the two thermo- 

 elements form part of a closed circuit. A horizontal scale (K, K) is placed at a 

 distance of 3 metres from the mirror, so that the divisions of the scale are seen in 

 the mirror. The scale itself rests upon a telescope (F) directed towards the mirror. 

 The observer (B) who looks through the telescope can see the divisions of the scale 



