NA TURE 



[June 28, 1906 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.] 



Kew Publications. 



As 1 was responsible before I left Kew for the publi- 

 cations noticed in Nature of June 21 (p. iSo), perhaps I 

 may be permitted a few words of explanation. 



The Kew Bulletin was not intended at the outset to 

 rank with scientific journals. It was started at the desire 

 of Parliament for the purpose of issuing, for public use, in- 

 formation for which there happened to be a demand, and 

 of a commercial, or at any rate economic, kind. It was 

 subsequently decided by the Government that it should be 

 the vehicle for other matter, scientific or otherwise, for 

 which prompt publication seemed desirable. 



It is sent out to all the botanic and agricultural depart- 

 ments in correspondence with Kew in India and the 

 colonies, and much of its contents is usually reprinted in 

 the local journals. 



It also serves the purpose of expeditiously answering 

 inquiries at home. A stock of the numbers is kept at Kew 

 for communication to correspondents. So useful has it 

 proved in this way that it has been necessary to reprint 

 more than once a large number of the articles. The out- 

 put in any one year may have been exiguous ; but if there 

 was no urgent demand for information on some new sub- 

 jects, there was usually more pressing work on hand than 

 the mere manufacture of padding. As, however, the 

 Bulletin is filed in many libraries, I was glad to have the 

 leisure to put the successive annual volumes into a ship- 

 shape form. When the ne.xt general index is issued the 

 whole series of volumes will form a sort of rough, though 

 necessarily incomplete, encyclopaedia of practical inform- 

 ation on Indian and colonial agriculture and products. 



The announcement of appointments mav have been be- 

 lated, but that again is of little consequence, as they are 

 onlv intended to be items in a continuous record. 



The catalogue of portraits was not supposed to be ex- 

 haustive, and does not compare, therefore, with the " Cata- 

 logus Stockholmiensis." It is simply a hand-list for the 

 use of visitors of the portraits exhibited in Museum No. i. 

 The Kew collection has always been popular, and, as I 

 know of no other, is " probably unique," but it has latterly 

 grown out of all bounds. As the available space was re- 

 stricted, I made a selection, and, so far as prints were 

 concerned, had them uniformly framed. I was guided by 

 considerations which I have stated in the preface, and I 

 confess I was largely influenced for the purpose of public 

 exhibition by artistic mSrit. Mere trivial photographs and 

 cuttings from illustrated papers, though valuable so far as 

 they go, seem to me most conveniently preserved in port- 

 folios. 



The personality of those who have made a mark in 

 scientific history has, I think, a peculiar, because intimate, 

 interest. The world is certainly the poorer for having no 

 portrait of Gilbert White. Only recently I have seen the 

 posthumous portraits of two distinguished men of whom 

 no memorial now remains which bears the impress of 

 vitality. 



In the seventeenth and eighteenth centuries few men 

 of any note disdained to transmit their portraiture to 

 posterity by the aid of the engraver. It was not, indeed, 

 until the middle of the last century that the practice expired 

 in the more feeble art of the lithographer. .Some examples 

 of its decadence I felt obliged to withdraw as painful 

 caricatures. Nowadays, modesty or indifference seems to 

 leave neglected all but the most eminent. I am not with- 

 out hopes that more space may be found at Kew for 

 portraits. I hope the collection may continue, as in the 

 past, to be the recipient of gifts from private liberality, 

 and that in this way many obvious gaps may be filled up. 

 W. T. Thiselton-Dyer. 



Witcombe, Gloucester, June 25. 



NO. I913. VOL. 74I 



A Remarkable Lightning Discharge. 



The afternoon of Saturday last, June 23, was sultry, 

 and It was therefore without surprise that about 8.30 p.m. 

 we observed the reflection in the clouds of lightning to 

 the west and south-west, and heard from time to time 

 the low sounds of distant thunder ; there was no indication 

 of the storm coming near to us until 9.30 p.m., when we 

 were startled by a tremendous explosion and a brilliant 

 flash of light, vifhich, according to some observers, was 

 continued after the explosion took place. This explosion 

 was, I think, the loudest that I ever heard, and the 

 impression on all of us was that It was quite close, and I 

 am told that it was heard nearly two miles off as if it 

 was close at hand. The thunderstorm continued for some 

 hours after this explosion, but never came near to us. 



It was not until the ne.xt morning that we discovered 

 the scene of the explosion of the fire-ball, if such was the 

 nature of the agent. 



In one part of the garden here there is a mound — the 

 remains of an old greenhouse — of irregular form and 

 height — on the northern side grown over with ferns, ivy, 

 and weeds, from which, towards its western end, grows an 

 ash tree of moderate size, which gives out its first branches 

 between 16 feet and 17 feet from the ground. The leaves 

 of the tree seem Intact, but the Ivy of the trunk, from 

 immediately below the branches down to the mound, has 

 been more or less stripped of its leaves ; a space half round 

 the tree has been disturbed, and the weeds and plants 

 thrown down, very much as if they had been trampled 

 down by human feet ; and this disturbance is continued 

 in a line down the mound on the northern side, the plants 

 being depressed from above downwards, and the gravel 

 path at the foot of the mound broken up more than half- 

 way across. Many of the leaves of the ivy have been 

 scattered about, and many of the leaves lying on the 

 mound have been torn to pieces. Several pieces of dead 

 wood on the mound have been broken asunder. A branch 

 of ivy close to the root of the ash tree has been stripped 

 of Its bark ; an old brick lying on the mound under the 

 vegetation was broken into four pieces, two small pieces 

 and two large of nearly equal size ; one of these larger 

 pieces was found on the mound, one was found about 

 7 feet 6 inches from the point at the foot of the mound 

 where the disturbance was seen, one smaller piece was about 

 7 feet beyond this, and another yet 2 feet further beyond 

 the last. A piece of highly-crystalllsed Old Red Sandstone 

 lying on the mound was found with a new and unweathered 

 exposure several inches in length, and fragments of the 

 same stone with new faces were lying near. 



The conclusion from these facts seems to me to be 

 that the electric agent, whether a fire-ball or not, must 

 have approached the ash tree in a nearly horizontal line 

 and struck it just below the lowest branches, have passed 

 down the tree to the mound, have disturbed the vegetation 

 to the south of the trunk of the tree, have passed then 

 towards the north down the mound, and then to have 

 nearly crossed the garden path, when it disappeared. 

 When exactly the explosion took place I feel at a loss to 

 ascertain, but perhaps some of your readers may be able 

 to assist in determining this point. Edw. Fry. 



Fniland, near Bristol, June 25. 



Tbe Magnetic Inertia of a Charged Sphere in a Field 

 of Electric Force. 



Dr. O. Heaviside has investigated (Nature, April 19) 

 the slow motion of a charged conducting sphere through 

 a uniform electric field, in a direction parallel to the 

 electric force of the field, and has calculated the Increase 

 in the magnetic energy and Inertia of the sphere resulting 

 from the re-dlstribution of the charge under the influence 

 of the field. His paper has suggested the following in- 

 vestigation, in which the slow motion of the sphere is 

 at right angles to the direction of the electric field. But, as 

 Dr. Heaviside has pointed out to me, this problem has no 

 single definite solution. For, if the sphere, initially at 

 rest In the field, be set in motion, the motion of 

 the unequally distributed charges on the surface of the 

 sphere will tend to give rise to magnetic force In the 

 interior ; but the magnetic force will only gradually pene- 



