On the Psychrometer and Chemical Hygrometer, 525 



faint ring of the bulb in A was observed. Instead of placing 

 an exhausted bulb in T, a coil of four turns with its ends 

 joined through 100 was laid on T ; and the bulb in A adjusted 



Fig. 12. 



A one turn ; S, R, and T each four turns. 



to give a very faint ring ; on removing the coil from T a 

 decided brightening of the discharge in the bulb was observed. 

 This experiment seems to show fairly conclusively that in- 

 creasing the energy in the circuit of the secondary S dimi- 

 nishes the brightness of the discharge in the bulb placed in A*. 



LIII. Comparative Experiments with the Dry- and Wet-Bidb 

 Psychrometer and an improved Chemical Hygrometer. By 

 M. 8. Pembrey, M.A., M.B., Radclife Travelling Fellow; 

 late Fell Exhibitioner of Christ Church, Oxford. (From the 

 Radclife Observatory, Oxford.)^ 



DURING the late winter it seemed desirable to make a 

 series of comparative experiments with the Dry- and 

 Wet-Bulb Psychrometer and an improved Chemical Hygro- 

 meter, in order to ascertain the accuracy of the results given 

 by the Psychrometer for temperatures below the freezing- 

 point. 



A series of comparative experiments, made by me in the 

 summer of 1889, had shown that the amounts of moisture 

 calculated from the psychrometric readings varied by -f 6 per 

 cent, to —5 per cent, from the amounts actually found by the 



* Since writing the above the author finds that Prof. J. J. Thomson 

 has observed the effects noticed in the second experiment, and gives an 

 explanation practically identical with the above. 



t Communicated by Mr. E. J. Stone, F.E..S., Radclifte Observer. 



