14 



KNOWLEDGE 



[January 1, 1900. 



lytic action, combustion, and violent evaporation were 

 doubtless all present. I further suggested that the 

 assistance of Botanists was required for the complete 

 solution of the problems. 



In the October number of Knowledge a most in- 

 teresting letter from Baron Kaulbars was published. 

 Here much detail was given concerning the fate of 

 various trees, as also an account of the destruction of 

 a stone monument which was, at intei-vals, braced in- 

 ternally by iron angles. But strangely enough the 

 writer, in giving his conclusion (which, to save space I 

 will write " steam ), altogether overlooks the terrific 

 force in Xature — Electro-chemical action. Further, 

 while he says that a very old dry tree may be burned 

 down he seems to overlook the fact that the insulator 

 i-esin is highly inflammable. Again, one finds it diffi- 

 cult to suppose that in the case of the tower the path 

 of the lightning was from iron to iron. If however 

 this was actually so, we are confronted with a remark- 

 able difficulty to which I shall refer later. 



Next, in November last, Lord Hampton, after en- 

 dorsing the statements made by Baron Kaulbars, states 

 that upon one occasion (of which details are given), 

 Faraday, pronouncing upon a smitten tree, asserted that 

 the lightning had gone down the hollow stem and, 

 meeting with damp at the bottom, generated steam, 

 so causing an explosion. Now, with all deference, I 

 would submit that there appears to be an error here. 

 Faraday knew well enough that the resistance of air is 

 enormously higher than that of any wood. By air I 

 mean of course air at more or less normal pressure. 

 Why then did the lightning seek the path suggested ? 

 We must regard trees as being in a measure lightning 

 conductors. This brings me to the undeveloped argu- 

 ment suggested by the case of the tower which Baron 

 Kaulbars mentioned. Did the lightning follow a track 

 (which was in all probability tortuous) through each 

 piece of iron, going always from one to that next it ? 

 I doubt it. But of this more anon. 



A few days since the Editors handed me two letters 

 which they had received recently upon this question. 

 The first, signed E. W. Mitford, gives very many instan- 

 ces of trees having been struck. His first case is that 

 of an Elm, and the damage done he describes as having 

 been via " several serpentine channels through the bark, 

 and reaching half way up the tree from the ground.' 

 Now this serpentining is not difficult to account for (it 

 was mentioned in October), the fact being that the 

 current goes from point to point by the easiest route. 

 But why the suggestion of '' from the ground " ? The 

 idea of return shock, or earth's potential is difficult of 

 conception here. A tree may easily enough be struck, 

 first, half way up its height, and further, there cannot 

 be much doubt that the trees are less susceptible to 

 damage (of a serious natui'e) at their tops. The same 

 correspondent remarks that he has frequently seen 

 lightning rise in a tapering pillar from the earth. This 

 is no doubt the so called " Luminous Rain. " Oh that 

 I had space to deal with it here ! ! 



The next letter is that of " An Old Rug." May his 

 hearth never grow cold ! ! He, dating from Jamaica, 

 tells how the top of a tree was taken off and earned 

 away with tremendous violence. The branches too were 

 cut off and strewn round a hole in the earth where the 

 root had been. (I want in this connection one detail — 

 was the hole lined wi'-h earth in its normal condition. 

 or was there a sleeve of vitrified sand ?) The trunk of 

 the tree was completely shattered. That is to say here 

 again the top was only injured by removal. 



Finally, in the December issue, P. de Jersey Grut 

 gave particulars of a case which is perhaps more in- 

 teresting than any yet cited. In this instance the tree 

 struck was encircled by a rope some twenty-five feet 

 from the ground, and it so chanced that an end of the 

 rope stood out from the bark of the tree, so that during 

 the earlier part of a rain-storm the tree was damp 

 from +he top to the rojie, while the lower portion of the 

 trunk was kept comparatively dry. The tree in this 

 condition was struck, the lower part only being 

 damaged. And the damage followed, downwards, a 

 path which the twist in the fibre of the wood made 

 easiest. 



And now, endeavouring to gather up those thread 

 ends which I am painfully conscious of having scat- 

 tered; the methods of lightning seem erratic. The 

 word "chance" is all too often misunderstood; it 

 really means the natural effects of causes which were 

 unexpected, or even unknown. And lightning moves at 

 a speed that is literally beyond our ken, save for figures 

 which convince only the few. 



From all this then, I propose, in conclusion, to ven- 

 ture upon one or two Isold statements. Suppose an 

 enormously powerful magnet to have been erected, 

 several feet above a building, and further suppose that 

 the surrounding air be filled with flying masses of 

 steel moving " lil e lightning. " What would be the 

 result? Would the steel that came near go to the 

 magnet? Some might, but, remembering the pre-sup- 

 posed (lightning) velocity many of these masses would 

 swerve from their paths if they were sufficiently near, 

 and go crashing through the roof. In other words, a 

 lightning conductor may often bring destruction just 

 near enough to destroy that which it has been set up 

 to protect. And a tree top may bring the lightning 

 to its own immediate neighbourhood, yet, not quite to 

 itself, so that it is not extraordinary if the tree be 

 struck in the middle. 



I am painfully conscious that I have not done jus- 

 tice to my subject. But, as a lightning conductor, I 

 seem to have drawn towards me a vast deal of (may 1 

 say matter ?) with which I cannot deal. Careful ob- 

 servation, and well recorded data are still at a premium. 



ILtttcrs, 



[The Editors do not hold themselves responsible for the opinioLS or 

 statements of correspondents.] 



'• IS THE STELLAR UNIVERSE FINITE ?" 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — In his interesting papers on the above sub- 

 ject in Knowledge (July and November), Mr. Burns 

 has neglected three factors which, I think, must be 

 taken into consideration. These are (1) the absorption 

 of light by our atmosphere, and (2) by our object- 

 glasses or mirrors, and (3) the finite sensibility of our 

 eyes and photographic plates. 



Suppose for a moment that all .stars consists of two 

 degrees of intrinsic brightness, their differences in 

 photometric magnitude being otherwise due to differ- 

 ences in distance, and that stars are uniformly distri- 

 buted through space. Then with a given aperture we 

 are able to see every star within a sphere the radius of 

 which is equal to the greatest distance at which a star 

 of the second (the fainter) degree of intrinsic bright- 

 ness can only just be seen by reason of the three 

 factors mentioned. Outside this sphere we have a 



