558 



Prof. H. L. Callendar on Electrical 



terminals marked d C 2 (for compensator) so as to be in 

 series with the adjustable plug resistances denoted by R in 

 the annexed diagram of connexions. The compensator leads 

 are connected in series with the Balancing Coil, denoted by S 



Fig. 11, 



Rheostat 



Tkerm 



Diagram of Connexions for Thread Recorder. 



in the diagram, to the terminals marked Pj P 2 . With this 

 arrangement the resistance S + C is nearly constant, so that 

 if the galvanometer deflexion is adjusted to be correct when 

 the thermometer is at 0° C. or 20° C, or any convenient 

 temperature, the scale will be very nearly correct when the 

 thermometer is at any other temperature, the plugs R being 

 suitably adjusted. 



As an example of the adjustment of the galvanometer 

 scale, we will suppose that the thread recorder is properly 

 set up and levelled, and the zero adjusted to the right hand 

 side of the scale, which reads from right to left. The standard 

 type of record sheet is divided into 25 scale-divisions, with 

 a heavy line at each fifth division. With this sheet it is 

 most convenient to adjust the scale to read 5 divisions to 

 1° C, giving a range of 5° C. on the record sheet. 'Suppose 

 that the thermometer has a resistance of 26 ohms at 0° C, 

 and is adjusted to have a fundamental interval of exactly 

 10 ohms, giving a change of 01 ohm per 1° C. Suppose 

 that the balancing resistance S is 30 ohms and is adjusted 

 to be equal to the thermometer at 40° C. Ten centimetres 



