224. 



♦ KNOWLEDGE ♦ 



[Sept. 12, 1884. 



"Lot Knowledge grow from more to more." — Alfbed Tennysob. 



Only a small proportion of Letters received can possiily he in- 

 serted. Correspondents must not le offended, therefore, should their 

 letters not e/ppear. 



All Editorial communications should be addressed to the Editor o» 

 Knowledge ; all Business communications to the Pdelishebs, at the 

 Office, 74, Qreat Queen-street, W.C. If this is not attended to 



DELAYS AEISE FOB WHICH THE EdITOB IS NOT BESPONSIBLE. 



All Remittances, Cheques, and Post Office Orders should be made 

 payable to Messbs. Wtman & Sons. 



The Editor is not responsible for the opinions of correspondents. 



No COMMUNICATIONS ABE ANSWEEED BY POST, EVEN THOUGH STAMPED 

 AND DIBECTED EKTELOPE BE ENCLOSED. 



SHOOTING STARS AND METEORITES. 

 [1389] — It seems to have been formerly assumed, without 

 inquiry, that shooting stars and meteorites are identical. It is not, 

 therefore, very surprising that subsequent investigators, finding 

 that there were no sufficient grounds for this assumption, should 

 have concluded that they were wholly distinct. This, for instance, 

 is the opinion of the distinguished Astronomer Royal for Ireland, 

 Dr. Ball. It seems to me that this is going too far in the opposite 

 direction, but I rather vrrite to elicit your opinion and that of 

 some of your distinguished correspondents than with a view of ex- 

 pressing a strong opinion of my own. Dr. Ball thinks that the 

 shooting stars which enter our atmosphere are vaporised before 

 they reach the earth. This is probably true of some of them. 

 Others, I should think, from the angle at which they strike our 

 atmosphere, shoot through it without vaporisation (though perhaps 

 heated so as to become luminous), and emerge with little altera- 

 tion on the other side. But supposing that the shooting star is 

 vaporised, what becomes of it afterwards ? It can hardly be sup- 

 posed to form a permanent addition to our atmosphere, for the 

 heat required to vaporise it will no longer exist after its 

 motion is arrested. The most natural result would seem 

 to be that the vapour thus created should solidify in fine dust 

 (seeing that the vapovir must be very rare when gene- 

 rated) and fall on the earth in that condition. And 

 this, perhaps, may be the origin of some of the dust- 

 showers which have been attributed to terrestrial volcanic agency. 

 But though, of course, the vaporisation of the shooting star, as 

 it is called, would increase the resistance to its motion, considering 

 the great speed of these bodies it might fail to arrest it altogether. 

 The vapour might continue to move, get clear of our atmosphere, 

 and soUdify again outside of it. In this, however, it is evident 

 that its orbit would be materially altered. The earth's attraction 

 and the resistance of the atmosphere would coerce it to travel in a 

 new course quite distinct from its former one, and in much nearer 

 proximity to our earth. The same observation would apply to a 

 shooting star which had passed through a section of our atmosphere 

 without vaporisation. Its proximity to us and the resistance of 

 the portion of the atmosphere which it encountered would alter its 

 course materially, and even perhaps make the earth rather than the 

 sun the centre round which it moved for the future. This might 

 occur though the star had not actually entered our atmosphere, or 

 had not entered it tar enough to become luminous. The shooting 

 stars, whose orbits were thus altered by the earth's attraction, 

 would approach it more closely in their subsequent visits, and their 

 motion would experience further retardation at each collision with 

 the atmosphere ; and in this way it seems to me that they might 

 finally drop to the earth without being heated to Itmiinosity at the 

 time of the actual contact. They would, moreover, before this 

 period arrived, cease to be identified with any particular group of 

 shooting stars. They would have wandered so far from the 

 original course of the Leonids, the Perseids, or the Andromedes, 

 to which they had once belonged, that their origin could no longer 

 be distinctly traced. But that genuine shooting stars — highly in- 

 candescent bodies — have fallen to the eai'th at certain times can 

 hardly, I think, be doubted. Thus the " fire-ball " whose course 

 Dr. Ball traces in his treatise on astronomy must, I think, have 

 fallen into the sea not far from the Scilly Isles, and it seems to have 

 presented all the prominent chai'acteristics of a shooting star. Why, 



then, should we seek for the origin of meteorites in volcanoes on 

 the earth or the moon if shooting stars which have been once 

 brought tmder the influence of the earth's attraction, and thus 

 diverted from their former orbits, will account for them Y 



W. H. S. MoscK. 



BRILLIANT 3IETE0R— SILENT LIGHTNING. 



[1390] — On the 3rd of July, 1884, a very brilliant meteor was 

 seen all over eastern Ontario and northern New York. I was at a 

 pic-nic at the time. The sun had set, but there was plenty of 

 light in the sky. The meteor nearly followed the equator from 

 east to west. Its colour was bluish white, and it suddenly burst 

 like a rocket when about 20° above the horizon. It looked so close, 

 that my first impression was that one of our party had let off a fire- 

 work. After bursting, a line of light about 8° long marked the 

 latter part of its track for fully fifteen minutes. It was at first 

 straight, but gradually broke up into a serpentine shape, like bo 

 much smoke. 



From comparison with its apparent track, as seen at other places, 

 it appears to have passed over the northern part of the State of 

 New York. 



Last summer I was travelling in Nebraska and Colorado during 

 very thundery weather, and several times noticed flashes of 

 lightning in clouds almost overhead, without any sound following. 

 On one evening in particular these silent flashes in a cloud at an 

 altitude of about 60' were almost continuous for nearly an hour. 



While in Nebraska I witnessed a hailstorm which completely 

 destroyed all the crops over a tract seven miles by two. The 

 stones were the size of large plums, and were driven nearly hori- 

 zontally by a violent wind. This happened on the evening of a 

 very hot, still day. Uusafib. 



DEAN SWIFT AND THE SATELLITES OF MAKS. 



[1391] — In connection with " Simplex's " quotation from Swift 

 anent the Martian moons, may I be permitted to give a rough 

 version of M. Flammarion's racy comments on the same subject in 

 " Les Terres du Ciel " (Paris: 1884). Having quoted from "Gul- 

 liver," as " Simplex " does, the brilliant Frenchman proceeds ; — 

 " Here truly is fiction singularly like truth. The prophets of the 

 Bible were never so clear about Christ, and in inspiration Swift is 

 the superior of Daniel and of Jeremiah. Something for weak- 

 kneed theologians to think over. Had some archaeologist found an 

 inscription to that effect in the ruins of Egypt or Assyria, those 

 who venerate the past would not fail to have concluded that our 

 ancestors had optical instruments of enormous power. However, 

 it is certain that neither Kepler, nor Swift — nor Voltaire, who 

 writes to the same effect in his delightful "Micromegas" — had 

 seen the Martian moons, and that theirs was merely a happy 

 thought. We, in our turn, might conclude that Uranus had 16 

 satellites and Neptune 32; but it is likely that here reasoning from 

 analogy would lead us astray from the truth." Abthue Mee. 



[In so far as M. Flammarion's argument is directed to showing 

 that the coincidence betiveen the mention of a previously unsus- 

 pected fact, and the subsequent discovery of its objective existence, 

 may well be a mere coincidence and nothing more, it is quite legiti- 

 mate. I protest, however, against one, at least, of his iUnstrations 

 as irrelevant. To wantonly and offensively attack what has been, 

 and is, held sacred by some of the best and wisest men the world 

 has yet seen, is neither science nor common sense. — Ed.] 



FALSE PERSPECTIVE. 



[1392] — I perceive that the rudiments of perspective still engage 

 the attention of your correspondents. 



Their opposed views may be grouped into two classes. To one 

 order of minds there appear — firstly, an object ; secondly, an eye 

 to see it with ; and, thirdly, a mental picture. The physical picture 

 is like Banquo's ghost, not discernible by two people in one place at 

 one time. To the other order of minds there is a fourth factor in 

 the case — namely, a physical picture outside the eye, not at all to 

 be confounded with the mental picture within. 



Letter 1359 in your No. 146 iUnstrates the triple factor system 

 exceedingly well. T. E. (R.) Jones contemplates certain posts as 

 external objects, and acknowledges certain appearances or seemings 

 to the inner consciousness. For instance, he says " the post at a 

 will appear taller," &c. ; but he has no word to say about the 

 relation of the appearances to the physical picture, considered as a 

 stubborn fact, equally objective and external to the eye, with that 

 other external matter which artists call the subject of the picture. 



Your correspondent's strong line A B cannot be the picture, 

 because it does not intercept any lines of light travelling in direc- 

 tions between the posts and the observer at A. Adopting his 

 illustration as regards the posts, I will superadd three different 



