18 



ready strongly emphasised, is abnormal. How, then, could 

 vapour be the main cause ? How is it that the aqueous 

 vapour of our atmosphere never before (to my knowledge, at 

 least) assumed this peculiar state? If there was such an 

 abnormal amount of vapour high in the atmosphere as to give 

 rise to sunsets and sunrises which by their wondrous beauty 

 have astonished both savage and civilised men, at least no 

 known factors in terrestrial meteorology could possibly have 

 first occasioned it. Moreover, I shall show from my own ob- 

 servations that the spectroscope has denied the existence of 

 this vapour on occasions of some of the finest sunset displays. I 

 see no objection, however, to the main dust theory, and it can, I 

 consider, equally be held under the hypothesis of either cosmic 

 or telluric dust. Each is equally tenable, but analysis of col- 

 lected material can only determine the truth. It is known 

 that some 10,000,000 meteorites enter our atmosphere daily, 

 their matter being dissipated in dust in the higher regions, at 

 an average height of twenty to forty miles. This meteoric 

 matter is trifling when compared with the volume of the at- 

 mosphere itself, which is said to weigh 5,178,000,000,000,000 

 tons, while only 182,500 tons of ordinary meteoric matter are 

 precipitated yearly, if we take, according to Prof. Laugley, an 

 average of 500 tons of meteoric dust cast into our atmosphere 

 each day. But the earth, as Mr. Eanyard supposes, may have 

 encountered a huge meteoric zone of dust, which augmented 

 to a vast extent the normal dust envelope with which we are 

 surrounded. 



Now, what are the objections to this theory of abnormal 

 cosmic dust? First, Mr. Ellery, considering the major 

 diameter of our elliptical orbit, declares it must be impossible, 

 since such a zone must have a breadth of about 183,000,000 miles. 

 This certainly appears to upset the hypothesis of cosmic dust. 

 But let us for a moment consider. Our entire system, with its 

 diameter of some 5,491,996,000 miles, is but an atom lost in 

 the immensity of space ; our gigantic sun, with his diameter of 

 852,900 miles, a star of the Milky Way, resembling in physical 

 constitution, as the spectroscope proves, others of the so- 

 called "fixed stars" oE the Kosmos. 



I ask, then, is it unthinkable that our entire system, in its 

 lightning speed through space, should have encountered some 

 gigantic zone of cosmic material enveloping the whole of it ? 



Next it is supposed that any cosmic material would be con- 

 sumed by the heat of impact. Of this it is, I think, impos- 

 sible to speak positively, as the amount of consumption and 

 dissipation would bear a ratio to the velocity of impact and of 

 the meteoric dust-belt, and such would probably offer little re- 

 sistance to the atmosphere, being extremely fine and impalp- 



