296 



NA TURE 



[January 25, 1906 



Praslin. Its palms are either male or female, and our 

 examination of more than 300 of its nuts showed that they 

 are of two distinct, structurally different forms in approxi- 

 mately equal proportions, both kinds growing on the same 

 female tree. The case is, so far as I know, unique. 



Of the land animals we did not attempt to collect the 

 birds, as they were already sufficiently known. Moreover, 

 most of the peculiar Seychelles species' would seem to have 

 been nearly, if not entirely, destroyed bv paid collectors. 

 Ihe Government of the Seychelles has, however, promised 

 an ordinance to hinder further destruction. The intro- 

 duced birds do not belong to the jungle, where, indeed 

 land birds are seldom seen. Mammals are represented by 

 rats, mice, and bats, and the tenrec runs wild everywhere. 

 Of reptiles we obtained about eleven species of lizards 

 and three snakes. The crocodile would once seem to have 

 been a regular inhabitant, but the last was killed about 

 seventy years ago. Three of the apparently four species 

 of frogs occur at any elevation, but the fourth is peculiar 

 to the high jungles. Ccecilians are numerous, the one 

 genus being an earth burrower, and the other lying under 

 damp leaves in the jungles. Mollusca were represented 

 among the indigenous vegetation bv twenty-five to thirty 

 species, including two slugs, and we obtained a fair variety 

 of insects and arachnids. Isopods were numerous every- 

 where, but centipedes and millipedes were scarce on the 

 high lands, and seemed to consist of species peculiar to 

 1 hem. We carefully searched for Peripatus, but do not 

 think it exists in the archipelago. Land worms were 

 scarce ; one species was peculiar in living within the 

 bases of the screw pine leaves, even 40 feet to" so feet above 

 !li.> ground. We obtained no land leeches or furbellarians 

 but found two species of Nemerteans at about 2000 feet. 



The fresh-waters consist of certain pools near the sea 

 and a large number of tiny mountain streams, which be- 

 come roaring torrents in the wet season, but never dry up. 

 In a pool at La Digne we obtained one tortoise with hinged 

 plastron, and in the streams there were four species of 

 fish. Ihe Crustacea comprise at least two species of prawn 

 ami a crab, all living up to more than 2000 feet The 

 Mollusca number only three, and for the rest there were 

 the usual genera of fresh-water insects, &c. 



The number of species of land and fresh-water animals 

 would on the whole appear to be singularly few and 

 individuals were, with a few exceptions, by no means 

 abundant. I heir small varietv may be due to the com- 

 paratively few plants which grow in the islands but one 

 is inclined to question the former connection of the group 

 with any larger land mass. In any case, our work lias 



made certain that the an lago has been sufficiently 



collected lor a thorough examination into this question 

 from a biological point of view. It is our opinion how- 

 ever, that such a research should include both animals and 

 plants considered together. In any case, the Seychelles is 

 the continuation of a broken line extending north from 

 Madagascar, and its rock would seem to be similar to that 

 which forms the great central plateau of that island 



Since I returned to I ngland 1 have received a letter 

 from Commander Boyle Somerville giving the soundings 

 "'"■""'"l by II. M.S. Sealark on her return to «..,,/„ 

 lnin V ' Seychelles. lie has confirmed by additional 

 soundings the complete separation of the 2000-fathom lines 

 the Chagos, Maldive, and Seychelles groups. I have 

 a ' so hear d from Mr. D. Matthews thai 'he has obtained 



,""" ' samples of sea-water from the Indian Ocean 



during the last nine months, and analysed about 700 Mr 

 Bainbr.gge Fletcher, II. M.S. Sealark, reports thai a con- 

 able number -if the Chagos Lepidoptera appear to be 

 new species or varieties. 



-,,-,,, J- Stanley Gardiner. 



Zoological Laboratory, Cambridge, January 1;. 



What Causes the Destructive Effects of Lightning? 



I ENCLOSE a cutting from the Hampstead and Highgate 



Express (January 20) containing an epitome of a lecture 



which I lateL gave at the local scientific society on a case 

 of death by lightning which occurred on the Heath in the 

 month of July last. 



I dismissed, amongst other matters, the question as to 

 how the more destructive effects ol lightning were pro- 

 duced, and now my object in writing to Nature is to ask 



no. 189 1 , vol yx] 



you, Sir, or any of your readers, if you can inform me 

 whether this question has been solved in anv probable 

 manner. In the case of the death of an animal from 

 lightning I think we may safely rest on the word elec- 

 tricity as sufficient, for it is not difficult to understand 

 how this form of energy when let loose in the organism of 

 an animal should not only disturb the equilibrium of the 

 machinery, but actually stop it. But the word electricity 

 does not seem sufficient to account for the more destructive 

 effects produced by lightning, which closely resemble those 

 which arise from other well known allied forces. Heat 

 certainly is produced, as we see by the burning of the flesh 

 and by its effects on metals, but as regards the destruction 

 of trees, buildings, and other imperfect conducting sub- 

 si. on. is, the forces seem to be of an explosive character, as 

 are mentioned in the accompanying extract Irom my 

 lecture. 



" The subject which was of most interest to the lecturer 

 was the nature of the destructive agency of the lightning 

 flash, and the present fatal case he thought threw a con- 

 siderable light upon it. Of course, there was no difficulty 

 in understanding how an electric shock can kill an animal 

 suddenly by bringing the machinery to a stop, when it is 

 considered how fearfully and wonderfully we are made, and 

 that vital processes are at work in every part, when a 

 violent electric shock comes and arrests all these at once. 

 But it is not so easy to perceive how all the more marked 

 and mechanically destructive processes occur, such as the 

 splitting of the timbers in the hut or tearing off the 

 clothes. The destructive effect seemed to be exactly of the 

 kind which follows explosions of gunpowder and kindred 

 substances. This could only occur through a gas being 

 suddenly formed ; but whether this would be the produc- 

 tion of the vaporisation of a liquid or the formation of 

 some new conditions of the atmosphere by the electricity 

 itself cannot at present be determined. The first object 

 struck by the lightning was the finial, and this was split 

 into numbers of pieces in the direction of the grain of the 

 wood, and the same effect was seen on all the upright 

 posts down which the lightning ran ; but, midway across 

 the middle of the hut was a transverse beam, through 

 which the flash passed. At this spot about a foot of the 

 wood was torn off, but in a transverse or horizontal direc- 

 tion in the course of the grain. If a chisel had been 

 driven into the cross beam it would have broken the wood 

 exactly in the same manner; or, indeed, any other force 

 acting on the middle of the splintered wood as an explosive. 

 The coat, and more especially the shirt, showed the ex- 

 plosive force which had produced the rents still better. 

 Although the rents ran down the arm, they had no appear- 

 ance as if done by an instrument, but rather by a violent 

 pull exerted from side to side, for not only was there one 

 large rent, but similar partial ones running parallel to it. 

 These could only have been done by forcibly stretching 

 from within; in fact, the only way suggested would be an 

 explosion of gas taking place in the shirt sleeve, and so 

 forcibly thrusting it out, causing ihe fibres ..I the fabric 

 lo give way. The split boot, which was nearly off the 

 foot of the child, could not be imitated except by placing 

 .1 charge of dynamite within it." 



Not professing to have much knowledge of what has 

 been written on the modes and causes of the great de- 

 struction caused by lightning, I am writing to obtain more 

 information on the subject. SAMUEL Wilks. 



January 20. 



The Probable Volcanic Origin of Nebulous Matter. 



In papers published some fifteen years ago (see, among 

 others, Nos. 2 and 4 of Contributions from Ihe I. id; 

 Observatory) I considered certain phenomena produced by 

 streams of finely divided matter ejected from the sun, each 

 stream necessarily taking on the form of a helix, and 

 stated that the nebulosities surrounding certain stars were 

 probably caused by the presence of streams similar to those 

 which produce the solar corona. 



In an effort to explain the fact that in certain spiral 

 nebulas two diametrically opposite streams are, as a rule, 

 most conspicuous, Prof. Chamberlin advanced the theory 

 -.-.■ Astrophysical Journal for [901, p. 17) that the dis- 

 ruption of one body through tidal action and centrifugal 



