KNOWLEDGE & SCIENTIFIC NEWS. 



[DnCEMBliR, UJO5. 



chiefly at the following side of the spot, which has drifted 

 far East relatively to the rotation of gh. 55m. 19s., repre- 

 senting the normal rate. 



While writing I may note that the present autumn 

 has furnished many excellent observing nights. 

 Between October 7 and 14 the weather was very 

 cloudy, but between October 15 and November 11 

 there were 22 nights clear and 6 overcast. On quite a 

 large proportion of the clear nights planetary definition 

 was found very sharp. This was especially the case on 

 November 6, when I tried powers of 713,912, 1210, and 

 1540 on my i2i in. reflector. The details could be well 

 seen on Jupiter' with the latter power; but the difficulty 

 of getting the image into the field, and keeping it there, 

 rendered the use of lower powers much preferable. 



W. F. Denxi.ng. 



Bristol, November 13, 1905. 



Note or\ the Absorption Lines of 

 Wa-ter Va-povir. 



0.\ comparatively rare occasions the spectrum of sun- 

 light exhibits very pronounced absorption lines due to 

 the atmosphere being very highly charged with water. 



These rainbands are particularly prominent in that 

 portion of the spectrum which contains light of wave- 

 lengths between .000059 and .oooofK> centimeters, i.e., 

 in the region extending towards the red from D about 

 one quarter of the way to a 



When the pKJsitions of these bands are well known 

 they may be detected as faint lines when the air is less 

 heavily laden with moisture, but if the moisture is 

 excessive they form, after the sodium lines, the most 

 prominent features of the spectrum in the region 

 indicated. In London such occasions of excessive 



°ua 



AVSOKPTION 



1 



absorption occurred on June 17, 1902, June 6, 7, and 9, 

 and .September 6, 1905, and they were taken to fix the 

 position of the prominent bands as indicated in the 

 drawing. 



At 59.20 and 59.26 occur two bands, each of them 

 triplets; at 59.45 occurs another triplet, ff)llowL-d by 

 five doublets, the last (A which is at 59.82. The atmo- 

 spheric conditions being favourable the best time for 

 the exhibition of these bands is in the early morning in 

 summer, picking np light from a low point in the I-^ast. 

 However, in June of this year there was nf) difficulty in 

 obtaining them at :my hour and at any altitude on the 

 6th and 7th day of that month. 



Unsettled weather always accompanies these 

 strongly-marked bands, and their existence certainly 

 forms a very trustworthy warning of a bad day. 



T. H. B. 



The Zodia.ca.1 Light. 



\\\ Akthlk Mee. 



Mr. Mal .\uek has well shown in his " .X.slronomy 

 without a Telescope," that an object which requires 

 no instrument to study, which most people can see if 

 they try, and which has been observed for countless 

 generations, still remains to a great extent a mystery. 

 The object is the Zodiacal Light, that nebulous cone 

 which appears in the west after sunset in early spring, 

 and in the east before sunrise in late autumn, and 

 which, bright in the tropics, may still be profitably 

 studied in our less favoured latitudes by anyone whose 

 horizon is not troubled by the glare of artificial light. 



Kepler, long ago, came to the conclusion that the 

 Zodiacal Light was an appendage of the sun, and his 

 opinion has on the whole, received the confirmation of 

 modern observers ; but much more remains to be done 

 before all the necessary data have been secured, data 

 which in no way depend on the telescope, but must Ix; 

 collected by naked-eye observers, aided by the virtues 

 of accuracy and patience. 



It is not our purpose here to deal with the methods 

 of observing and studying the light. These are dealt 

 with fully in the charming work above referred to. 

 But we desire to call attention to some very interesting 

 observations just made by Dr. .Simon Newcomb, the 

 eminent American astronomer, which indicate, so far 

 as they go, that the Zodiacal Light lies to the north 

 and south of the sun as well as to the east and west of 

 our great luminary. Prior to Dr. Newcomb's ob- 

 servations no attempt has ever been made with success 

 to observe the Zodiacal Light to the north of the sun; 

 in fact, the feat is one presenting a good deal of dilli- 

 culty. 



To begin with it cannot be done when the sun is 

 less than 18° below the horizon, on account of the 

 interference of twilight, nor must iS" be exceeded to 

 any great extent else there would not Ix; enough of the 

 light left above the horizon to be seen. In fact (as 

 Newcomb points out), unless the minor semi-axis of 

 the light considerably exceeds 18" it may be for ever 

 impossible to distinguish it from twilight itself. The 

 observation may best be made in latitudes such as our 

 own, but there must in addition be .'i perfectly clear 

 horizon, and the more elevated the post of observation 

 tlie better. Dr. Newcomb tells us that even in the 

 liear air of the United St:ites he has so far failed, a 

 fact which, in itself, indicites that the observation is a 

 most delicate one, demanding not (jnly a trained eye, 

 but the most perfect of local conditions. 



Whilst in Hurope this summer the distinguished 

 astronomer determined to try his experiment amongst 

 the mountains of .Switzerland. Me therefr)re consulted 

 a Swiss scientist, who advised the Brienzcr Rolliorn, a 

 summit suitably situated, easily .■iccessible, and nearly 

 S.ooo feet high. Thither Dr. N'ewcomb repaired on 

 July 26, and made <areful observations on that evening 

 and also on the 29th. 



At 10 o'clf)ck on the first of the evenings in ques- 

 tion the twilight had completely passed, but there was 

 a faint glow over the north-western horizon whii:h, 

 twenty minutes later, was 20" west of north. It after- 

 wards became well marked, and was watched mitil the 

 haze thickened and put an end to observation. 



