324 



Dr. M. Maclean. On the Effects of Strain 



view when I started these experiments. The arrangement is shown 

 diagrammatically below. One junction of the wires was kept in a 



glycerine bath which could be heated by a Bunsen burner. This 

 junction was tied by a fine copper wire to the bulb of a ther- 

 mometer T. The other ends of the wires were joined to short copper 

 wires which served as terminals of the low resistance galvanometer 

 used in the experiments. These junctions were wrapped in paraffin 

 paper or cotton wool which contained the bulb of a thermometer T', 

 reading half degrees from 0C. to 25 C. A paper screen S was hanging 

 vertically between the Bunsen burner and the thermometer T' and the 

 galvanometer to prevent any heat from the flame reaching the rest of 

 the circuit by radiation. These precautions were taken to make 

 certain that all junctions, except the hot junction, would be at the 

 same temperature. 



6. The constant of the galvanometer was determined by joining a 

 Daniell cell in circuit with the galvanometer and with a resistance of 

 over 30,000 ohms. The electromotive force of the Daniell cell was com- 

 pared with a standard Clark cell by means of a quadrant electrometer. 

 In this way the current through the galvanometer per division deflec- 

 tion on the scale was determined. The sensitiveness, in preliminary 

 experiments, was 0-612 mikroampere per division. But by different 

 arrangements of the controlling magnets, the sensitiveness of the 

 galvanometer as now used is 0*09 mikroampere per division. The 

 resistance of the galvanometer, at 15 C. the average temperature of 

 the laboratory during the experiments is 1:5 ohms. Thus the electro- 



