72 Dr. Meyer Wilderman on the Velocity of 



their temperature varies o, l, and is o, 00001 for a variation 

 of o, 01. As long as the coils are immersed in a homogeneous 

 liquid — not in a heterogeneous system, where the warming of 

 the liquid e. g. is prevented by the very rapid process of 

 melting of the solid solvent, &c. — the coils cannot by simply 

 stirring the liquid be kept constant more than to a few 

 hundredths of a degree. In my paper (Phil. Mag. Dec. 1897) 

 I have shown that in one of the most developed freezing- 

 point methods lately published even the equilibrium of ice 

 and water is affected by errors which amount very nearly to 

 0°*01, so that we must not overrate the result we can obtain 

 by bath-regulation only, unless quite extraordinary arrange- 

 ments are made. 



The Berlin Reichsanstalt conducted currents of different 

 intensity from a thermopile through a coil, and measured the 

 deflexion of the galvanometer, rapidly reversing the current. 

 The results obtained were : — 



Q. T-T x =d. E. 



Inair 1 watt 9'5 0"00037 



In petroleum 1 l'l 0*0022 



10 6-7 0-0035 



50 25*0 0-0048 



„ „ 100 41-0 0-0055 



Here Q is the transformed energy in watts in T — T x = d, 

 T is the temperature of the wire, T x of the surrounding- 

 medium (air or petroleum), E is the quantity of heat given 

 up through 1 cm. 2 , when T-T^l . They also found that 

 in petroleum the wire acquires a constant temperature within 

 about a minute, whilst in air only after half an hour to 

 an hour had elapsed. In some of my publications of 1896 I 

 have already shown that a beaker with 1250 c.cm. water 

 is cooled down in a liquid bath about twenty times more 

 quickly than in the air. 



To keep the coils at a constant temperature, and to avoid 

 the heating effect of the current, the coils of the resistance- 

 box have been immersed in 6 litres of petroleum, contained 

 in a double-walled copper vessel with an air-space between 

 them. The copper vessel could be heated by flame or kept in 

 a thermostat if required. The coils have been covered with 

 shellac, repeatedly annealed, and all placed by Mr. Fisher in 

 the same plane so as to secure equality of their temperature. 

 For the same reasons, my platinum coil, as will be shown 

 later, is always immersed in the liquid itself. Prof. Callendar 

 and Mr. Griffiths have the coils of their resistance-box also 

 immersed in petroleum, their platinum coil, however, still 



