90 HALLEY S COMET: PHYSICAL OBSERVATIONS. 



Tabe III. — Continued. 



(4) spectroscopic Examination of the Light from the Sky. — • 

 All that could be done in this direction consisted in directing 

 a wave length spectroscope towards the sky, near to the sun, 

 and observing whether any lines appeared to become more 

 intense, special attention being directed to the neighbourhood 

 of the Coronium line. Nothing definite could be recorded. 



(5) Presence of Dust in the Air. — In order to collect any 

 fine particles which might have been brought into the atmos- 

 phere by the comet, an experiment was made by drawing air 

 for twenty-four hours through a series of twelve glass bulbs 

 containing distilled water, all with several plugs of well- 

 washed cotton wool in order to catch any dust. The water 

 left in the bulbs was carefully evaporated in a platinum dish 

 and the vessel tested for radioactivity. Only a very slight 

 trace was obtained. There was a small deposit of a very fine 

 red substance seen upon the cotton wool in the first bulb, 

 but it was ultra-microscopic and probably consisted of the 

 usual atmospheric dust. 



(6) Spectroscopic Examination of the Air. — Samples of air 

 were taken in an exhausted tube furnished with stopcock and 

 electrodes. The tube was rapidly exhausted by a Fleuss pump 

 to about I mm. and the spectrum examined when a discharge 

 was passed through the tube. A chart had been prepared 

 on which the principal spectrum lines had been marked and 

 the lines observed in the spectrum were plotted upon this. 



Observations were taken on the 17th, i8th and 19th from 

 4 p.m. on the i8th to 5 a.m. on the 19th, at intervals of an 

 hour. The spectra in all cases were coincident. A quantity 

 of about 1*5 litre of air was collected in an exhausted bulb; 

 the nitrogen, oxygen, etc., being removed by sparking over 

 caustic potash. The residue showed the spectrum of Argon, 

 the red lines being very distinct. A line in the yellow, due to 

 Neon, could also be recognised, but no trace of Helium. 



A similar experiment was made with gas collected on July 

 3rd, and this yielded an identical spectrum. We may conclude 

 that no new gas was introduced by the comet into the atmos- 

 phere. 



All the experiments have thus yielded negative results, and 

 if the comet's tail actually did envelope the earth it certainly 

 did not produce any marked chemical or physical change in 

 the atmosphere. A sharp look-out was kept for meteors, but 



