ASTRONOMY. 407 



gressive marcb renders the cosmic origin of these particles quite im- 

 probable, for in case of a cosmic origin there seems to be no reason why 

 the phenomenon should not appear nearly simultaneously at all i)oints 

 on the earth's surface. Those regions on the Indian Ocean forming the 

 trajectory of a cyclone show in a convincing manner that the ashes of 

 the Java volcano, caught up by the ordinary winds of that quarter, are 

 the cause of the extraordinary sunsets in question, 



" The objection may be raised that the height of these particles is 

 very great in comparison to the height to which the smoke of our Euro- 

 pean volcanoes rises; but, after reading M, Verbeck's report, these 

 • objections disappear before the greatness of this volcanic convulsion. 

 A quantity of matter, whose volume was estimated at 150 cubic kilo- 

 meters, was seen projected 18 or 20 kilometers above the crater. When 

 we think that the gaseous matter that escaped at the same time must 

 represent a volume some hundreds of times as great, we cease to be 

 astonished at the thought of the diffuse dust reaching an altitude of 70 

 or 80 kilometers. As to the suspension of these particles in the air, it 

 at least does not contradict what we know of the laws of the air's vis- 

 cosity, nor of the action of winds, heat, and atmospheric electricity. 



"A more detailed discussion of the documents published on the sub- 

 ject of this frightful explosion would carry us beyond the scope of this 

 simple article ; enough has been said to show that these optical phe- 

 nomena, of which our atmosphere has been for some eighteen months 

 and is still the scene, may be referred with great probability if not cer- 

 tainty to a volcanic origin." (Cornu, in Bull. Astron., April, 1885.) 



The Moon : Lunar heat. — At the Albany meeting of the National 

 Academy of Sciences in October, 1885, Professor Langley read a paper 

 "On the temperature of the surface of the moon." 



Attempts were made in the last century by several i)hysicists to ob- 

 tain indications of heat from the moon, but without success. Professor 

 Forbes, in 1885, employed a lens by which the lunar heat was concen- 

 trated about 6,000 times, but obtained no certain evidence of heat, be- 

 ing led only to the negative conclusion, that the warming effect of the 

 full moon on the surface of the earth would, at any rate, not exceed 

 30WO0 of a degree, Centigrade. Tlie first satisfactory evidence of actual 

 heat was obtained by Melloui in 1846, who, with a polyzonal burning 

 lens, one meter in aperture, and by the aid of^ the newly invented ther- 

 mopyle, in the clear air of Vesuvius, after due precaution against in- 

 strumental error, succeeded in obtaining decisive indications of heat, 

 although the amount was all but immeasurably sinall. Later observers 

 were also able to do little more than detect evidence of the existence of 

 lunar heat, and the first attainments of anything like quantitative 

 measurement thereof, was reserved for Lord Eosse, whose experiments 

 are recorded in the proceedings of the Eoyal Society, commencing in 

 1869. The paper now before us details the experiments by Professor 

 Langley, at the Allegheny Observatory, with the instrument invented 



