542 



NA TURE 



[August io, 1905 



while Mr. Fletcher, paymaster, and Dr. Simpson are 

 collecting the insects and land plants. I may say at once 

 that the latter are of the type which one would expect 

 lO find on purely oceanic islands, but their distribution 

 from island to island is interesting, as well as their pre- 

 ferences for sand or rock, drought or moisture, &c., most 

 of the islands having definite zones with their peculiar 

 plants. 



" It is really as yet too early to say anything about the 

 reefs here, as there are one or two places which I have 

 not yet been able to visit. What strikes one, however, 

 very forcibly is the comparative absence of life on them. 

 Of course there are in places plenty of corals, but the 

 number of species is quite limited. There is a fair number 

 of the usual Alcyonaria, but Sponges, Hydroids, and Tuni- 

 cates are very few in species and in quantity. Turbellaria 

 are very rare, while Molluscs, Echinoderms, and Crustacea 

 are few in species and, except certain common forms, not 

 numerous. Ptychodera we have obtained, as well as a 

 few Sipunculids, but Amphioxus and Thalassema we have 

 not found. At Minikoi in two tides I have brought to 

 the camp as great a variety of animals as Cooper and 

 1 have obtained here working ten tides up to the present. 

 Indeed, life here is strictly limited in variety, and, when 

 the marine collections have been fully worked up, one is 

 inclined to anticipate, even so early, that some definite 

 light will be thrown on the distance to which the larva? 

 of marine animals can cross the open ocean, on the dis- 

 tribution, in fact, of marine animals. The same, too, is 

 true as well of the marine plants, nuUipores alone being 

 common. 



" I am now endeavouring to work up the physical con- 

 ditions of the atoll so as to find, if possible, whether there 

 is any physical cause for the comparative paucity of free- 

 living animals. 1 am sending Cooper in the ship to- 

 morrow to Diego Garcia, where he will have four or five 

 days while she is coaling to examine the land and reefs. 

 I remain here, but I hope by the time of his return, in 

 about twelve days, to have finished my work and to move 

 on to Peros Banhos, while the Sealark is sounding between 

 the banks and round the Chagos Archipelago." 



The Problem of the Random Walk. 



I H.\\'E to thank several correspondents for assistance 

 in this matter. Mr. G. J. Bennett finds that my case of 

 n = 3 can really be solved by elliptic integrals, and, of 

 course. Lord Rayleigh's solution for n very large is most 

 valuable, and may very probably suffice for the purposes 

 I have immediately in view. I ought to have known it, 

 but my reading of late years has drifted into other 

 channels, and one does not expect to find the first stage 

 in a biometric problem provided in a memoir on sound. 

 From the purely mathematical standpoint, it would still 

 be very interesting to have a solution for n comparatively 

 small. The sections through the axis of Lord Rayleigh's 

 frequency surface for n large are simply the " cocked 

 hat" or normal curve of errors tvpe ; for n = 2 or 3 they 

 do not resemble this form at all. For n = 2, for example, 

 the sections are of the form of a double U, thus UU, the 

 whole being symmetrical about the centre vertical corre- 

 sponding to c=o, but each U itself being asymmetrical. 

 The system has three vertical asymptotes. It would be 

 interesting to see how the multiplicity of types for ii 

 small passes over into the normal curve of errors when 

 n is made large. 



The lesson of Lord Rayleigh's solution is that in open 

 country the most probable place to find a drunken man 

 who is at all capable of keeping on his feet is somewhere 

 near his starting point ! Karl Pe.^rson. 



Proposed Magnetic and Allied Observations during 

 the Total Solar Eclipse on August 30 



In response to my appeal for simultaneous magnetic 

 and allied observations during the coming total solar 

 eclipse, cooperative work will be conducted at stations 

 distributed practically along the entire belt of totality and 

 also at outside stations, nearly every civilised nation 

 participating. 



These observations will afford a splendid opportunity 

 for further testing the results already obtained. All those 



NO. 1867, VOL. 72] 



who are able to cooperate are invited to participate in 

 this important work. 



The scheme of work proposed embraces the following ; — 



(i) Simultaneous magnetic observations of any or all 



of the elements according to instruments at the observer's 



disposal, every minute from August 29, 22h., to August 30, 



^h., Greenwich mean astronomical time. 



[To ensure the highest degree of accuracy attainable, 

 the observer should begin work early enough to have 

 everything in complete readiness in proper time. See 

 precautions taken in previous eclipse work as explained 

 in the journal Terrestrial Magnetism (vol. v., p. 146, and 

 vol. vii., p. 16). It is essential, as shown by past experi- 

 ence, that the same observer make the readings through- 

 out the entire interval.] 



(2) At magnetic observatories, all necessary precautions 

 should be taken so that the self-recording instruments will 

 be in good operation, not only during the proposed interval, 

 but also for some time before and after, and eye readings 

 should be taken in addition wherever it be convenient. 



[It is recommended that, in general, the magnetographs 

 be run on the usual speed throughout the interval, and 

 that, if a change in the recording speed be made, every 

 precaution possible be taken to guard against instrumental 

 changes likely to affect the continuity of the base lines.] 



(3) Atmospheric electricity observations should be made 

 to the extent possible by the observer's equipment and 

 personnel at his disposal. 



{4) Meteorological observations in accordance with the 

 observer's equipment should be made at convenient periods 

 (as short as possible) throughout the interval. It is 

 suggested that, at least, temperatures be read every fifth 

 minute (directly after the magnetic reading for that 

 minute). 



(5) Observers in the belt' of totality arc requested to 

 take the magnetic reading every fifteen seconds during 

 the time of totality, and to read temperatures as frequently 

 as possible. 



(6) At those stations where the normal diurnal variation 

 cannot be obtained from self-recording instruments, it is 

 desirable to make the necessary observations for this pur- 

 pose on as many days as possible before and after the da\" 

 of the eclipse, and to extend the interval of observations 

 given above if conditions permit. In general, those who 

 will have self-recording instruments have decided to run 

 them for at least- eight days before and after the day of 

 the eclipse. 



It is hoped that observers will send full reports of their 

 work to me as soon as possible for incorporation in thi- 

 complete monograph on this subject to be published by 

 the Carnegie Institution of Washington. 



L. A. B.At'ER. 



Department Terrestrial Magnetism, Carnegie 

 Institution, Washington, D.C., July 15. 



British Fruit Growing. 



In your remarks on p. 297 (July 27) on the above sub- 

 ject, you mention " the diversity of yield from farms in 

 the same neighbourhood . . . due presumably to differ- 

 ences of shelter and aspect." It is a remarkable thing 

 that, so far as I know, nothing has ever been done 10 

 find out and publish the most suitable localities, as regards 

 soil and climate, for orchard planting. It is a question 

 of very great complexity, and can only be dealt with 

 properly by officials appointed for that purpose; but its 

 importance in fruit culture is so obvious that a consider- 

 able expenditure would be well repaid. Few peonle have 

 any idea of the great climatic differences in localities 

 within even a few hundreds of yards ! 



This house is on the south slope of the long range of 

 Lower Greensand hills which runs parallel with' the Chalk 

 range the whole length of Kent from west to east. At 

 this point the slope rises steeply from 200 feet above 

 sea-level to 500 feet, my house being about 350 feet. I 

 have carefully observed the effects of frost, &c., for the 

 last six years, and it appears to me that the variations 

 in temperature in the vertical limits mentioned are much 

 greater than would be expected. L'p to the 400-feet con- 

 tour line the climate is singularly equable, which is nroved 

 not only by daily thermometrical observations, but by the 



