382 Professor C. Piazzi Smyth's 



serve in the economy of nature, in a medium which the che- 

 mists tell us they find consists of exactly the same propor- 

 tion of oxygen and nitrogen all over the world, at all heights 

 in the atmosphere, and all times and seasons 1 a convincing 

 proof this of the rudeness of chemical analysis when it tells 

 nothing whatever of the existence of millions of atoms which 

 optical examination shows to be existing in every cubical 

 foot of air. Whether the presence of these particles be 

 for good or evil on organized beings, we may be quite certain 

 that they are decidedly bad for astronomical observations of 

 the more delicate description, and can be fortunately over- 

 come to a very great extent by erecting observatories on high 

 mountain stations ; for the result of long experience on the 

 Trigonometrical Survey at the Cape of Good Hope, went to 

 show that this atmospheric dust is chiefly confined to a height, 

 according to the season of the year, of from 3000 to 6000 feet 

 above the surface of the earth, often preserving a very dis- 

 tinct upper surface to the stratum ; and all mountain tops 

 rising to a sufiicient height to appear above it, were seen with 

 a clearness and distinctness that seemed almost irrespective 

 of distance, more like that of the celestial spaces, where we 

 may assume, for such observations, that there is no inter- 

 vening medium, or that, if there be, it is perfectly/ transparent. 

 Observations of the Surface of the Sun. — More continued 

 and regular observation of the changes on the surface of 

 the sun than has generally been the case hitherto, is much to 

 be desired, and should be prosecuted, together with the search 

 after the external phenomena of the red flames. When 

 large spots appear for a time, sudden attention is called 

 to them, and for the instant a number of persons accumulate 

 observations of them, but after a little while drop the 

 subject altogether. But the existence of spots of some sort 

 or other must be taken as the rule, rather than the ex- 

 ception ; and the omission of a single day's observation of 

 them may be the loss of an important link in the chain of 

 evidence required for the formation of any theory concern- 

 ing them. But to pursue the case with rational prospect of 

 success, we must evidently take all the varied phenomena 

 on the sun's surface into account at once — the red promi- 



