404 



ME. J. H. BRINKWORTH ON THE SPECIFIC HEAT OF STEAM AT 



in these experiments have been compared with No. 7 at various dates, and the 

 differences between this cell and any individual cell have remained small and approxi- 

 mately constant. The differences expressed in hundredths of a milli-volt, between 

 any cell and No. 7 are given in the following table, the negative sign indicating the 

 amount to be subtracted from the E.M.F. of cell No. 7 in order to obtain the E.M.F. 

 of the cell in question. 



From the last three sets of observations it will be seen that the cells used in these 

 experiments have remained constant to 1 part in 10,000 over a period of nearly four 



years. 



The Potentiometer. 



This was of the well-known Thomson- Varley pattern with two dials, its total 

 resistance being 100,000 ohms. The current for the potentiometer was supplied by 

 Leclanche cells, the number employed being adjusted in accordance with the magni- 

 tude of the electric current in the main circuit, to make the potentiometer readings 

 greater than 5000. The galvanometer used was of the Thomson pattern, having a 

 resistance of 7000 ohms, and the sensitiveness was such that a change of unit amount 

 on the vernier-dial of the potentiometer produced an alteration of 7 scale-divisions in 

 the galvanometer deflection. A calibration of the potentiometer showed that no 

 error amounting to 1 in 10,000 could be introduced by any arrangement of the 

 sliders. 



The Pressure Regulator (fig. 6). 



This was of the form designed by Prof. CALLENDAR, and exhibited by him at a 

 meeting of the Physical Society of London in 1902. It consists, essentially, of a 

 U-tube the limbs of which, lettered G and S respectively, are partially filled with 

 mercury. The gas after passing through a Wolff's bottle containing sticks of KOH, 

 to remove impurities in the gas, is led into the limb, G, through a tube, A, the lower 

 end of which is ground so that its cross-section is elliptical. The gas then passes out 





