94 



SCIENTIFIC NEWS. 



[July 2 7l 1888. 



CORRESPONDENCE. 



The Editor does not hold himself responsible for opinions expressed 

 by his correspondents, nor can he take notice of anonymous com- 

 munications. All letters must be accompanied by the name and 

 address of the writer, not necessarily for publication, but as v 

 guarantee of good faith. 



METEORITES AND LIGHTNING. 



At a recent meeting of the Royal Meteorological Society a 

 paper was read on "The Non-existence of Thunder-bolts," in 

 which it was sought to demonstrate that the fall of material 

 substances during thunder-storms, as being in any way con- 

 nected with the same, was a fallacy — a sophism that should 

 be relegated to the myths and superstitions of the past. 



I think, however, that there may be reasons for connecting 

 the two phenomena, and that a thunder-bolt, meteorite, aero- 

 lite — or whatever we may choose to designate the falling 

 substance — may occasionally he permitted to reach the earth 

 by the aid of an electric discharge. 



Recent researches have shown that about four hundred 

 millions of telescopic meteorites enter our atmosphere daily, 

 and become dissipated into vapour on reaching that part of 

 our aerial envelope which is sufficiently dense to raise the 

 temperature of these supramundane bodies to vaporising- 

 point. 



The pressure of our atmosphere at sea-level equals about 

 15J lbs. per sq. in., but, as the increment of elevation arith- 

 metically progresses, so the decrement of density and pressure 

 geometrically progresses ; thus, at three miles the pressure is 

 reduced to about 7J lbs , while at six miles it is but little 

 more than 3J lbs. ; beyond this height it must rapidly gradu- 

 ate into an etherial substance of extreme tenuity ; hence a 

 meteorite travelling towards us would meet with continually 

 increasing resistance owing to increasing speed and increas- 

 ing air density, so that the nearer it approached the earth the 

 less likely would it be to reach it. 



From the results of the observations made byEkholm and 

 Hagstrom, at Upsala, we find that clouds attain a higher alti- 

 tude than was formerly supposed. The highest cirrus clouds 

 observed reached 41,000 ft., the numerous other types being 

 found at varying distances below this. It was also observed 

 that the summits of cumulus clouds attained their greatest 

 height during thunderstorms, the bases of the same remain- 

 ing nearly always constant. 



It is supposed that clouds at a height of five miles consist 

 of crystallised water,and that the intense cold of such high 

 altitudes as 20 or 30 miles probably reaches 100° C. below 

 freezing point. 



From the above facts we may, I think, infer that certain 

 supramundane bodies are drawn towards the earth without 

 undergoing any change through friction or air-compression 

 during the first part of their journey ; let us assume also that 

 during the second stage the heat generated by an increasing 

 density of air would be counterbalanced by the intense cold 

 and clouds of frozen moisture, it must be apparent then that 

 after this stage the most formidable barrier would remain in 

 the shape of a rapidly-increasing density and temperature. 



In this last zone would be found a critical point, upon the 

 reaching of which the previously uninjured meteorite would 

 become incandescent and disappear. 



(I presume this critical point would vary considerably, de- 

 pending, of course, upon the nature of the meteorite and the 

 state of the surrounding atmosphere ; it would be interesting 

 to know, however, the nearest point to the earth at which in- 

 candescence has been observed to commence.) 



We now require to find some agent capable of dispersing 

 this final barrier of denser air : Now we know that an electric 

 discharge from any given thunder-cloud displaces the air in 

 its passage and forms pro. tetn. a vacuum ; we know, too, 

 that a discharge is not of necessity "forked," but that it may 

 reach the earth in the form of "well-refined ribbons or lines 

 of light ; " if, therefore, an aerolite were approaching us under 

 the conditions I have named above, and should enter a 

 thunder-cloud at the moment of an electric discharge, and in 

 a direct line with that discharge, is there any reason why it 

 should not escape dissolution by travelling in vacuo in the 



wake of such a discharge and reach the earth simultaneously 

 with it? 



Surely, we may assume that out of the millions of meteoric 

 bodies which enter our atmosphere some may occasionally 

 pass through the conditions I have indicated, and, reaching 

 the earth simultaneously with the flash, be designated veri- 

 table " thunderbolts." Cecil Carus-Wilson. 



Bournemouth, July 20. 



HABITS OF THE HESSIAN FLY. 



Last year we were told, on evidently good authority, that 

 the exceptionally dry, sunny weather had promoted the mul- 

 tiplication of this vermin to an extent not likely to recur 

 for some time. But this year we learn, on the authority of 

 Mr. F. Enock, F.E.S. — certainly an excellent observer — that 

 " the damp, muggy weather, is decidedly favourable for the 

 development of this pest." If both these views are well 

 founded, the Hessian fly must have a very accommodating 

 constitution. One Puzzled. 



A CIRCLE PROBLEM. 



Nothing can excuse my carelessness in copying 7896 instead 

 of the next figure 7926 from Whitaker. 



I am perfectly familiar with the algebraic demonstration 

 of this problem, but I did not send it to you in the first in- 

 stance until I found that a number of people who are equally 

 familiar were "caught" in thinking it to be more difficult, 

 or rather more tedious, than it really is. At the same time, 

 " Kuklos's " explanation of the " principle," as he calls it, is 

 — simple though it be — intelligible only to those who have 

 some acquaintance with algebra, while I endeavoured to 

 make it clear to "general readers." A. P. T. 



THE COSMICAL ORIGIN OF HAILSTONES. 



Replying to "F. M.," p. 70, I must refer him back to my 

 account of the formation of such hailstones. He will there 

 see that the conditions are such that they must be produced 

 simultaneously in countless numbers, forming clouds of ice 

 particles ; therefore must visit our earth under special condi- 

 tions, and in this respect differ entirely from the falling of 

 isolated meteoric stones. (I should add, by the way, that 

 the view there expounded of the modes of formation of the 

 hailstones is my own, suggested by Schwedoff's theory. I 

 have only read an abstract of his paper.) An encounter with 

 such a multitude of ice particles must of necessity produce 

 considerable atmospheric disturbance, especially in summer. 

 If such a cloud of hailstones entered the upper regions of 

 our atmosphere with any approach to planetary velocity, their 

 friction would bring. them into the condition of the particles 

 of water forming the cloud produced by Armstrong's hydro- 

 electric machine, which Faraday investigated experimentally, 

 proving that every particle of water therein was intensely 

 charged with positive electricity by its friction against the 

 jet nozzle and the surrounding air. Therefore, if I am 

 right, every terrestrial hailstorm should be accompanied with 

 "special terrestrial weather," i.e., usually with stormy 

 weather, and frequently with lightning, which is notoriously 

 the case, especially in summer. W. Mattieu Williams. 



THE LANTERN FLY. 



In reply to " An Old Entomologist " (Scientific News, 

 Vol. 1, p. 525),il beg to say that I have never seen an insect 

 vary its light, nor do I think that the different-coloured 

 light indicates a different species, as I have never de- 

 tected the slightest difference in the insects. The lights 

 are quite under the control of the insect, as it can shut them 

 off at pleasure, and when in captivity and at perfect rest 

 these lights are quite invisible, but immediately show up 

 as the insect is roused. T, 



