OF ARTS AND SCIENCES. 



53 



Note. — Between 74.5' and 25° the temperature rose too rapidly to obtain 

 intermediate readings with the air thermometer. 



.If these results are represented by a curve, of which the abscissas 

 are proportional to the temperatures, and the ordinates to the corre- 

 sponding electromotive forces, it is seen that the curve is approxi- 

 mately a right line for all the points except those corresponding to 

 the temperatures obtained .by tlie ether thermometer. It was to be 

 expected that these points would not lie exactly on the curve, as the 

 temperatures were so roughly obtained. 



The thermoelectric line for temperatures below 0° is almost a direct 

 continuation of the line above 0° ; the two, however, are inclined at a 

 slight angle. The reason of this is probably due to the fiict that for 

 temperatures above 0° the piece of electrolytic copper soldered to the 

 hot end of the nickel became more heated throughout than the piece 

 soldered to the cold junction ; and consequently the points of contact 

 where the copper galvanometer wires joined the two pieces of electro- 

 lytic copper were unequally heated, and a subsidiary current was pro- 

 duced. It was found that when both junctions of copper and nickel 

 were kept at the same constant temperature, a very small current 

 was produced when one piece of the electrolytic copi^er was slightly 

 heated above the other. 



From these experiments it appears that an ether thermometer can- 

 not be used to measure low temperatures accurately, not only because 

 the ether adlieres to the sides of the tube, but because its coefficient of 

 expansion is variable ; also that the thermoelectric line of copper and 



