158 



KNOWLEDGE. 



[Jri.Y 1. 1895. 



Dr. Keeler's famous observations on Saturn's rings have 

 begun to pass through the furnace of criticism. After 

 being generally accepted by laymen, they are not quite so 

 universally held to be conclusive by astronomers. M. 

 Deslandres, for instance, does not consider the kind of 

 evidence adduced by Dr. Keeler as any proof of the 

 meteoric nature of the rings, a theory which Clark 

 Maxwell first brought forward and the recent spectro- 

 scopic observations were supposed to confirm. 



Urttrvs. 



The Kditor does not hold himself respuiisible for tlie opinions ov 

 statements of correspondents.] 



• 



SUXSPOTS. 

 To the Editor of Knowledge. 



Sir, — In Knowledge for May, at pages 98, 107-110, 

 the magnetic perturbations of March 80th-31st, 1894, are 

 referred to the group of sunspots approaching the central 

 meridian on those days ; whereas these perturbations 

 were due to the disturbance at the sun's eastern limb at 

 the same time. The sun was likewise distinguished by the 

 presence of spots south of the solar equator, which is the 

 precise location most likely to be attended by auroral and 

 magnetic eflects near the vernal equinox. No matter what 

 spots appear elsewhere on the sun, whether great or small, 

 or east or west of the central meridian, whenever an aurora 

 appears a region specially frequented by spots will be found 

 at the eastern limb. In the case of the magnetic storms 

 and fine auroras of March 30ch-31st, 1894, there were 

 recurrences at the 27t[ day interval, both of the solar 

 conditions and of the attendant magnetic phenomena and 

 of thunderstorms, which followed precisely the order which 

 I have pointed out in various notes and articles, and which 

 is referred to in the recently published volume of the Inter- 

 national Scientific Series on the Aurora, by M. Angot. 



M. A. Veeder. 



New York, U.S.A., May 14th, 1895. 



MIBA-PRISMATIC COLOURS ON CL0UD3— MIEAGE. 

 To the Editor of Knowledge. 



Dear Sir, — If you can spare me space, I should like 

 to remark on the various observations made by your 

 correspondents. I can quite endorse Col. Markwick's 

 observations of Mira ; the light curve was quite unusual. 

 At the beginning of February it reached what should have 

 been its maximum of about 4th masnitude, or rather less, 

 and by the end of the mouth seemed inclined to fade ; but 

 during March it rose very suddenly again to about 3-5 

 magnitude (between "/ and 8 Ceti), as nearly as one could 

 judge in the twilight, on the 10th, and then fell quickly 

 again. 



I am also following R Leonis, but do not think any- 

 thing abnormal occurred. The maximum must have been 

 during the time of bright moonlight in March, for the star 

 was seen with the naked eye, with the full moon ia the 

 same constellation just before the total eclipse, and it 

 must have been 5th magnitude at the least. 



With regard to the prismatic coroufe and edges to 

 clouds, I may say that I have recorded them for some 

 years, and see them on the pearly white cloud streaks on 

 which they principally occur about twenty-five times in a 

 year. I look upon them as one of the most certain signs of 

 showery weather which we have, but halos are commonest 

 in dry, sunny seasons. Mock suns are commonest in the 

 spring, and are seen here about twelve times a year. 



One does not have to go to the Sahara to see a very fair 

 presentation of the mirage. They are common on dry, 

 sandy shores when the sun is hot, especially with an 

 easterly wind. A fortnight ago I saw a very good one on 

 Stert Flats, a wide expanse of sand in Bridgwater Bay. 

 On sitting down the sands seemed partly covered with 

 water, in which the opposite village of Burnham was 

 reflected, and I distinctly noticed that where red houses 

 occurred in the ' sea-front ' the colour was plainly imaged 

 in the mirage. So was a small white lighthouse standing 

 on the sands ; but the taller one standing back among 

 the sandhills did not appear. On standing up again, 

 the whole phenomenon disappeared. 



Bridgwater. H. Corher. 



THE SUN PILLAR. 

 To the Editor of Knowledge. 



Dear Sir, — In your June number the Rev. S. Barber 

 figures and describes a sun pillar seen in Cumberland on 

 the 30th January last. On the 10th Jlay a similar column 

 was visible here for about a quarter of an hour, beginning 

 at three minutes before 8 p.m. It had a delicate rose tint, 

 and a small bright shooting star seemed to spring from its 

 left side, and made a short trajectory. I suppose this was 

 an accidental coincidence. The column, I am told, was 

 seen at Eastbourne, but I have heard no particulars. On 

 the 12th May a fine solar halo appeared at 12.45, and was 

 visilile for half an hour. 



Forest Row, Sussex. Henry J. Slack. 



To the Kditor of Knowledge. 



Sir, — Mr. Barber's account of the sun pillar in yom 

 June number is most interesting, as it reminds me of a 

 similar phenomenon observed here by my father in 1868, 

 to which he called my attention at the time, and which 

 exactly agreed with your illustration. I find his notes 

 were as follows : — 



" April lOth. Sun column continuing half an hour after 

 sunset, which was perfectly bright without clouds." 



It occurred during a dry cold period, although a little 

 rain had been measured early that day. Wind N. — and 

 was succeeded by a wet period after the 18th. 



Yours truly, 



Further Barton, Cirencester. (Miss) E, Brown. 



THE COLOURS OF BUTTERFLIES. 

 To the Editor of Knowledge. 



Sir, — In your last issue Dr. Marshall has summarized, 

 and apparently adopted, the views of Mr. A. R. Wallace, 

 in regard to "the colouring of butterflies"; these views 

 being in support of the Darwinian doctrine of natural 

 selection. Dr. Marshall classifies his remarks under the 

 following heads, viz. : — 



Protective colours. — Referring to butterflies which are 

 protected by imitating the forms and colours of any 

 object on which they perch. 



\Var7ii7iii colours.— In which the colours of the butterflies 

 " are conspicuous for the purpose of warnimj other insects 

 (Wallace says enemies) to keep away." 



Miiiiicr;/. — " Many butterflies escape destruction by 

 mimicking the colours and the markings of the uneatable 

 forms." 



Ia all these cases it will be seen that it is inferred that, 

 while some butterflies are protected by their colouring, 

 there are others which are not so protected ; indeed, 

 Mr. Wallace expresses his wonder that, " with these great 

 resources at her command. Nature had not produced more 

 of these mimicking forms than she has done." 



