Oct. 6, 1882.] 



o KNOWLEDGE ♦ 



307 



remain still ozoniferous, and never can become entitled to 

 the term efirte, as the wind that comes to us from the 

 Continent always is. 



After floating over the Continent for days, and perchance 

 weeks, such a vast volume of air as blows over the narrow 

 sea between England and the Continent could scarcely 

 acquire in the short space of time occupied by its passage 

 a true marine character ; and evidence of this is seen in its 

 great dri/ness and the deficiency in what has been termed 

 ozone. For many years we took observations at all hours 

 and in a variety of localities, both inland and coastal, and 

 we invariably found that the east wind was defective in, if 

 not entirely free from, ozone. 



This want of the vivifying element of pure air, combined 

 with a want of moisture, we believe to be the cause of the 

 obnoxiousness of the east wind to all, and especially to 

 those who are delicate. We shall show, in a future paper, 

 how fatal it is in those parts of England that are not pro 

 tected from its malijrn influence. 



OF AN OBSERVATION NOT LONG SINCE 

 MADE IN ENGLAND OF SATURN. 



THIS Observation was made by Mr. William Ball, 

 accompanied by his brother. Dr. Ball, October 13, 

 1665, at six of the Clock, at Mainhead, near Exeter, in 

 Devonshire, with a very good Telescope near 38 foot long, 

 and a double Eye-glass, as the observer himself takes 

 notice, adding that he never saw that Planet more distinct. 

 The observation is represented by Figure 3, concerning 

 which the Author saith, in his letter to a friend, as 

 follows : — " This appear'd to me the present figure of 

 Saturn, somewhat otherwise than I expected, thinking it 

 would have been decreasing ; but I found it full as ever, 

 and a little hollow above and below. AVhereupou the 

 Person, to whom notice was sent hereof, examining this 

 shape, hath by Letters desired the worthy Author of the 

 Si/steme of this Planet that he would now attentively con- 

 sider the present Figure of his A uses or Rhig, to see 

 whether the appearance be to him as in this Figure, and 

 consequently whether he there meets with nothing that 

 may make him think that it is not 07ie body of a Circular 

 Figure that embrn'^p<! his Diuhe, but firo." 



And to the end that other Curious men in other places 

 mif;ht be engaged to joyn their Observations with him, to 

 see whether they can find the like appearance to that 

 represented here, especially such Notches or lloUownessos, 

 as at A and B, it was thought fit to insert here the newly- 

 related Account. — Philosophical Transactions, Vol. I. for 

 1665 and 1666, p. 152-3. (The engraving faces p. 155.) 



THE RAIN-BAND.* 



Br C. PiAzzi Smytu, Asteonomee Royal foe 

 Scotland. 



(Continued from page 291.) 



BUT if so much can be done by so small a spectroscope, 

 the questionmay be well asked whether more still might 

 not be accomplished with a bigger and more powerful one, 

 especially seeing that the dispersive powers of both chemical 

 and astronomical spectroscopes have in late years been in- 

 creased to a most astonishing extent The question is im- 

 portant, and somewhat new as well. I propose, therefore, 

 to devote the remainder of my space to its answer, rather 

 than to the practical rules for using the smaller instru- 

 ments, especially, too, as they have been already introduced 

 to the public, both by my friend, Mr. Rand Capron, in his 

 pamphlet, " A Plea for the Rain-band," and by myself, in 

 the fourteenth volume of the " Edinburgh Astronomical 

 Observations ;" also in the Journal of the Scottish Meteo- 

 rological Society, and in the September number of the 

 Astronomical Register for 1877. 



The greater part of higher power spectroscopes are not 

 suitable to rain-band work, for their fields are usually too 

 dark. But having recently built up for myself a large- 

 sized variety of the instrument, possessing perhaps the 

 greatest combination of power with transparency yet at^ 

 tained, and having it always mounted in an upper chamber 

 looking out at an altitude of about 5' over the north- 

 western horizon (or most suitably for rain-band work), I 

 will try to describe shortly its action therein. 



The classical " rain-band," which in the little instru- 

 ment is merely a very narrow fringe to an almost infinitely 

 thin black line, is so magnified laterally in the larger instru- 

 ment as to fill the whole breadth of the field. The thin 

 black line before spoken of is now not only split into two, 

 but each of these are strong, thick, sharply-defined lines, 

 separated from each other by six or seven times the breadth 

 of either. These are the celebrated Solar D lines, Dl and 

 D2 arising from the sodium metalloid burning or incan- 

 descent in the sun. They are, therefore, perfectly unin- 

 fluenced by changes of the terrestrial atmosphere, hot or 

 cold, wet or dry, and are, therefore, invaluable as references 

 for degree of visibility of the water-vapour lines and bands 

 which rise or fall in intensity precisely with those changes. 

 There are several of these earthly water-vapour lines and 

 bands in and between and about the D lines themselves ; 

 then a long breadth of band towards the red side of Dl ; 

 then a pair of lines not so widely apart as the D lines, but 

 sometimes just as sharp and black ; then two or three 

 fainter banJs ; then a grand triple, of which the nearer 

 line sometimes attains greater blackness than either D 

 line ; then beyond that three distinct, equal-spaced, isolated 

 bands ; and further away towards the red a stretch of faint 

 haze and haze-bands. 



All these go to make up the one thin rain-band of the 

 little spectroscopes ; and I fortunately had, through the 

 month of August and the early days of Sept<Mnber, oc- 

 cupied myself each morning in noting the greater or less 

 intensity of each, and all these water-vapour lines and 

 bands in terms of the i.wo Solar constants D 1 and D2 ; 

 and every such morning there was an abundance of details 

 to see, to recognise, and to measure. But on tlie morning 

 of Monday, September 1, when the little instrument had 

 truly enough marked on its very small scale, I almost 

 starU'd nt finding in the large instrument every member 

 of its long rain-band group, unless it were a vanishing 

 trace of one or two of the strongest, utterly gone ; while 

 tlie two D lines were in their accustomed strength, but 



