Reaction before Complete Equilibrium. 71 



are connected with the bridge and rheostat; A and C with the 

 battery, b and B with the galvanometer, K is a reversing- 

 key, Z is a contact- maker for battery and galvanometer. 

 Plate I. gives the outlines of a photograph taken from the 

 actual experimental arrangements of the method. 



I pass now to the description of all essential parts : — 



The Resistance-Box. — Prof. Callendar and Mr. Griffiths, 

 who, as known, have considerably advanced the subject, use 

 for their coils german-silver, which has a temperature- 

 coefficient of 0*00026 between 15° and 25° in terms of the 

 resistance at 20 u . 



Mr. Harker (Proc. Royal Society, 1896) uses manganin 

 coils suspended in air, the temperature of which is indicated 

 by a mercury-thermometer. The Berlin Reichsanstalt 

 found the temperature-coefficient of manganin to be about 

 0*00002. Messrs. Crompton and Fisher found that some 

 samples of manganin can be brought by repeated annealing 

 to a temperature-coefficient of a few in a million at about 20°. 

 The temperature-coefficient of my manganin coils Messrs. 

 Crompton and Fisher found to be 0*0000025 between 15° 

 and 25°. I found it somewhat higher, about 0*0000035, 

 i.e. the temperature-coefficient of my coils is about 100 times 

 smaller than that of german-silver. I presume the tem- 

 perature-coefficient of Mr. Harker's coils was also very 

 small *. 



The error arising from the coils is thus arranged : the 

 two arms A-B and B-C are practically equal (20 000 and 

 20*0001 ohms), and do not come into consideration, so that 

 the third arm only has to be considered. Since the tem- 

 perature-coefficient of the platinum coil is about 0*0036, that 

 of my manganin coils 0*0000035, the variations of the regis- 

 tered temperature due to the manganin coils is 0°*0001 if 



* The values of my coils were found with the potentiometer of 

 Crompton to be, when again measured January 1896 : — 



20(3) 20-000 



,'0(BC) 20-0004 



?0(AB) 19-0994 



10 10-0004 



5 5-0001 



3 30000 



1 -9997 



1 1-0003 



0-5 05000 



On comparison of the above data with these obtained by myself by 

 means of VVheatstone's bridge, using the standard of the Berlin Reichs- 

 anstalt, I found that the absolute values of the standard used by 

 Mr. Crompton are all somewhat (but proportionately) smaller than those 

 of the Reichsanstalt. 



