6ti Messrs. J. "W. Swan and J. Rhodin. Absolute [May 24, 



tight compartments. Jackets 1 and 2 were filled with water, and the 

 vessel 3 with paraffin oil having a flashing-point of 150 C. To stir 

 the liquids, three circular rings of iron wire were enclosed, one in 

 each of the compartments. These rings were suspended on the iron 

 wires, s l , s 2 , &c. The iron wires themselves were fixed on a bar of 

 brass, &. By means of the crank of an electromotor (?jt) and strings 

 and pulleys, the bar b could be moved up and down, stirring each of 

 the liquids simultaneously. To make the motion easy a balance 

 weight, W, was used. The coil to be measured was enclosed in com- 

 partment 3. This compartment was closed at the top by a hollow lid 

 of tinned iron, pierced with holes to allow for the passage of the 

 stirring rods, &c. This lid effectually protected the paraffin oil from 

 surface cooling. The two holes, h and h', made to allow the wires 

 connecting the ends of the coil to pass out, were lined with ebonite 

 to prevent contact with the metal of the lid. The thermometer, T, 

 was let down through a tube in the middle of the lid. As a proof of 

 the effectiveness of the arrangement, it may be mentioned that a small 

 Bunsen burner when burning at its full power, and placed under 

 compartment " 1 " raised the temperature of the inner one " 3 " only 

 0'1 C. in thirty seconds, a length of time more than sufficient for 

 making a resistance determination. When the temperature in "3" 

 tad been raised to 92 C. and then allowed to cool (being constantly 

 stirred), the temperature (in "3 ") only fell to 40 C. in twenty-four 

 hours, notwithstanding the temperature of the laboratory was only 

 15 C. 



Another important detail was an arrangement for securing the 

 wires whilst they were measured. Fig. 2 represents this. It consists 



FIG. 2. 



of a piece of ebonite tube 5 cm. diameter, with a deep double screw 

 thread cut on the outside. It was pierced all over with large holes 

 1 cm. diameter, to allow the paraffin oil to freely circulate in the 

 inside, where the thermometer was inserted. A short rod of ebonite 

 (p) was put through and across the cylinder at the bottom. The 

 wire to be measured was bent round this cross rod, so that equal 



