256 



KNOWLEDGE. 



[November, 1903. 



ihus appears to regulate the moou's position in the grfeat 

 meteoric phenomena, should also be illustrated ia minor 

 and irregular falls of Leonid meteors. Of all raeteor- 

 svstems the Leonids exhibit the best-marked periodicity ; 

 l>ut, as has been remarked by observers, shooting stars 

 from Leo may make their appeai-anee sometimes as much 

 as a week before or after the mean epoch. Such of these 

 minor or irregular displays as occurred before 1833 must 

 have lieeu by far the most remarkable, as they were not 

 specially looked for, and, therefore, must have been of 

 considerable splendour to have attracted casual observation. 

 Tn the following table the dates of these displays, mostly 

 taken from Arago's " Astronomic Populaire," Vol. IV., 

 pp. 308-312, are given with the time when the moon was 

 new or fiill and in perigee : — 



Prof. Kirkwood has given the date of the first of these 

 displavs, which he regarded as being connected with the 

 present mid-November meteor-system. Arabic chroniclers 

 mention the star-showers of 855 and 856 ; the shower in 

 the former year was also seen in Europe on the night of 

 October 17. The November star-shower of 1606 is thus 

 described : " On a bright night. November 15, 1606, it 

 seemed as though it rained stars ; tirst fell only the largest 

 and brightest stars from heaven, then indiscriminately 

 the large and small stars in great numbers" [quoted in 

 American Journal of Science and AHs, Vol. XXXVI. (2nd 

 Series), p. 301]. 



It is seen that in these fifteen showers the moon con- 

 formed, with biit one exception in 1823, to the rule shown 

 to prevail in the more brilliant phenomena ; the perigee, on 

 the other hand, does not conform with the same exactness, 

 and, as in the display of 93-J', the unusual position seems 

 to affect the intensity of these minor meteor-falls. The 

 peculiar position of the moon in all Leonid star-showers 

 cannot be explained as due to moonlight, for the latter 

 would as little diminish the splendour of a meteor display 

 two or three days before as at, or a few days after new- 

 moon, and woidd certainly be far less troul>lesome a couple 

 of days before full moon, than at or shortly after that 

 phase ; yet the moon in any of these great ancient or 

 modem star-showers is never found in the second or fourth 

 <|uadrants. It is remarkable that at the failure of the 

 Leonids to appear on November 15th, 1899, the moon was 

 within her second quadrant, and in her fourth at the 

 Leonid epoch of November 15-16, 1900. With the moon 

 in the first quadrant, moderately tine displays of Leonids 

 were seen in America on November 15 in the years 1898 

 and 1901. It is remarkable that the lunar conditions at 

 the Leonid epoch of 1766 resembled those of 1899, and 

 that there is no record of a shower having taken place in 

 the former year. The moon also happened to be un- 

 favourably, or at least unusually, placed for meteor 

 displays at the Leonid epochs of 1399, 1566, and many 



other occasions when important meteor-showers might 

 have been expected to have occurred. 



The conclusion which it seems to me is to be drawn from 

 the foregoing coincidences respecting the position of the 

 moon and the occurrence of Leonid star- showers, is that 

 there is a meteor-swarm revolving round our planet, and 

 that showers of shooting stars are produced from the per- 

 turbations of this meteor-ring under the combined action 

 of the sun and moon. The velocity of shootinc; stars must 

 be much lower than is generally supposed. Mathematicians 

 at first assigned these bodies a velocity of 200 miles per 

 second, a velocity that was subsequently abandoned only 

 when it was found that gravitation failed to account for 

 it. The heavier shooting stars, or bolides, have, however, 

 in well-authenticated instances, been found moving at the 

 rate of about 4 miles per second. 



Dublin, September 15th, 1903. 



John R. Henky. 



CUEIOUS SUNSET PHENOMENON. 



TO THE EDITORS OF KNOWLEDGE. 



SiES, — I think that the phenomenon described in the 

 September number of Knowledge by Lieut. Field must 

 be what is commonly called in Canada a " Sun-Dog " 

 We see them frequently in the winter, and usually 

 accompanied by cold weather. I have only noticed them 

 when the sun is a few degrees above the horizon ; some- 

 times the sun is obscured, as noted hy Lieut. Field, at 

 others the sun is shining brightly and there is merely a 

 slight haze of ice crystals. I think the Sun-Dog is a 

 branch of the phenomena classed under the general term 

 of ■' halos and ])arhelia,"' which are caused by refraction of 

 the sun's rays through floating particles of ice. Just why 

 the halo should take more than one form it is hard to say, 

 though I am inclined to think that the ice crystals, being 

 rhombohedral in form, would have a tendency to make 

 their " refraction products" more complicated than in the 

 case of the simpler raindrop ; one can imagine the ice 

 crystals all lying Ln one direction at one time and Ln 

 another at some other occasion, or having the sun's rays 

 refracted first through one layer of ice particles and then 

 through a second. 



At the elevation of Lieut. Field there would be every 

 chance of there being a screen of ice crystals between him 

 and the sun, although the temperature at the point i>f 

 observation was a long way above the freezing point. I 

 have often noticed a solar halo in the cirrus clouds when 

 the temperature of the surrounding air was above 32 F. 

 In bis case he was looking horizontally through the layer 

 of cold air ; in the case of the solar halo I refer to, one is 

 looking upwards. p^^rL A. Cobbold. 



Hailevbnrv, Ontario. Canada. 

 September 14th, 1903. 



THE PURPLE FLOWERS OF THE WILD CARROT. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — I find in one of the UmheUiferie, which I believe 

 to be Daucus, a single central floret of different colour 

 from the rest. I have to-day seen it pink and dark-red. 

 And in Scotland I was shown some that were dark blue or 

 purple. Is it usual, and does it occur in any other 

 members of the family r j; ^ Buechardt. 



Brashfield, Bicester, 



15th September, 1903. 



[The central flower, or several flowers, of Daucus Caroia 

 is frequently of a deep-red colour — generally, in fact, is 

 a well-deveioped umbel. No similar feature is found 

 in any other British umbellifer. I am not aware that 

 any explanation of this curious feature has been put 



