hallky's comet: physical observations. 



Table I. — Continued. 



On the 14th the maxima occurred at 7.45 a.m. and 7.30 p.m. 

 on the 31st at 9.15 a.m. and 7.15 p.m. 



No very unusual disturbance occurred between 7 a.m. on 

 the 19th. During- that time the comet changed its position 

 relatively to that 'of the earth and the sun, and if any passage 

 of the earth through the tail really occurred, it must have taken 

 place during the interval. 



(2) Conductivity of the Air.— A set of observations was 

 taken on the rate of leak of a charged electroscope. An 

 electroscope was fixed to the top of a metal chamber, and 

 through the latter a current of air could be drawn by a water 

 pump, or the air, after filling the chamber, could remain at 

 rest. ' From the electroscope a brass rod connected to the 

 gold-leaf system passed down into the chamber. The latter 

 was earthed so that any abnormal conductivity of the enclosed 

 air would increase the rate of leak from the electroscope. The 

 electroscope was charged and the rate of leak determmed by 

 a reading microscope with a micrometer in the eye- 

 piece. The deflection of the gold leaf being initially 

 50 scale divisions, it was found that the rate of 

 leak was about one division in five minutes when the 

 air was at rest, and practically the same when the air was 

 being drawn through in a continuous stream. The rate of 

 each was fairly constant during the three weeks, but on the 

 morning of the i8th there was a distinct change, as the follow- 



inu' table shows : — 



'^ Table II. 



Rate of leak of charged electroscope. Morning of i8th May, 19 10. 



Air at rest 



Time, 

 o 



5 

 10 



15 

 20 



25 

 30 

 35 

 40 



45 

 50 

 55 

 60 



