ASTRONOMY. 405 



favor (besides tbat of convenience in solar work) is, that there will be 

 established a certain uniformity of time-reckoning between astronomers 

 and the world at large. 



In addition to the references given above, we should call attention to 

 the following papers upon this important question : 



Ball (R. S.)- Proposed chaii^^c- iu tbo iistronoiiiical day. Observalory, 9 : 100. 



Fleming (S.). Uuiversal or cosmic time. Toronto [1H8.')]. 



FoERSTEU (W.). Ueber die vors der confercuz zu Washiugtou proponirte Veriindening 

 des astrouomiscbeu Tagesaufanj^es. Aslron. Xachr. 111:315-8. 



Letter from the Secretary of the Navy trausmitting communicatious couceruiug the 

 ])roposed cliaugo in the time for beginning the astronomical day [from the super- 

 intendent of the Naval Observatory, the superintendent of the Nautical Almanac, 

 and various American astronomers]. Senate Ex. Doc. No. 78, Forty-eighth Con- 

 gress, second session. 



Newcomb (S.). On the proposed change of the astronomical day. Month. Not. Foi/. 

 Astron. Soc. , 4"> : 12ii. 



VON Oppolzer (Th.) On the proposed change of the astronomical day. Month. Not. 

 Hoy. Astron. Soc, 45 : 295-8. 



Struve (O.). Die Beschlusse der Washington er Meridiancouferenz. St. Petersburg, 

 1885. 27 p. 8vo. 



'■^ Slcy-glou's : Certain phenomena in meteorological optics that have oc- 

 curred since the close of the year 1883. Hypothesis concerning the cause 

 and origin of these phenomena. — The immediate cause of the "red sun- 

 sets" seems to be the existence at a very great height in the atmosphere' 

 of a cloud, or rather a light mist, composed of very fine particles. This 

 hypothesis would explain the twilight phenomena when the sun was 18^ 

 or 20° below the horizon. We need not suppose these particles to have 

 had a greater altitude than 60 or 70 kilometers during the first of these 

 apparitions. 



" The red color of these lights corresponds very well with the absorp- 

 tive power of the atmosphere which physicists observe in the sun's 

 radiations at different altitudes and astronomers iu the ruddy tint pre- 

 sented by the moon's disk in total eclipses ;* the distance traversed 

 through the atmosphere by the sun's rays before reaching this cloud 

 explains sufiiciently the intensity of the coloring. 



" The solar corona and the anti-solar aureole could be easily explained 

 with this hypothesis if the particles held in suspension in the atmos- 

 phere are supposed to offer a sensibly constant mean diameter, as the 

 theoretical conditions for diffraction coronas would then be present. 



" The next question is, What is the origin of these particles suspended 

 iu the atmosphere? The reply to this question is quite independent of 

 the explanation of the phenomena of meteorological optics presented 

 above. There have been a number of hypotheses on this subject. The 

 first, seeking an explanation iu the ordinary domain of meteorological 



" The total eclipse of the moon October 4, 1884, did not show this red color in the 

 usual degree. This is regarded by some as a i^roof of the t'xisteuce of these clouds of 

 particles, the higher regions of the atmosphere being rendered less transparent by 

 their presence. 



