466 



NA TURE 



[March 14, 1901 



A further simplification would be introduced by a method of 

 evaluating the series Pj or Pj without the use of Stirling's 

 theorem. Such a method has been given me by Mr. G. G. 

 Berry, of Balliol College, and may be briefly described as 

 follows : — 



If in the expansion of {p + q)'^ we stop t terms before the 

 greatest, the truncated series has a smaller sum than the G.P., 

 which has the same two final terms. If t^ is great as compared 

 with n, the G.P. has a sum which vanishes compared with its 

 final term multiplied by >Jn. But the product of the greatest 

 term of {p^qT and sjn is finite; for the sum of Vw terms on 

 either side of the greatest <l, and the ratio of the greatest 

 term to a term distant from it by V« places is — 



\ pn) \ pnj \ pn ) 



qji 



which has a finite limit. 

 Oxford. 



Vll qn) \ qn) \ an' 



qn 

 J. Cook Wilson. 



A Tree Torn by Lightning. 



I ENCLOSE two photographs of an oak tree struck by light- 

 ning, which seem of interest. 



The storm, one of considerable violence, occurred on July 

 27, 1900, and continued for several hours. The tree stood by 

 the side of a road which runs over the Chilterns from Ipsden, 

 a little village about five miles from Wallingford and ten from 

 Henley. It was standing at the western edge of a small stretch 

 of woodland. The opposite side of the road was quite clear and 

 sloped down to the plain. 



On examination, the bark was found to be completely stripped 

 off and flung on one side ; a large branch was torn away, and 

 the fractured end was extraordinarily splintered and smashed. 

 So far as I saw there were no signs of charring. 



NO. 1637, VOL. 63] 



The inner surface of the bark was marked longitudinally with 

 thin wavy lines, very close-set, of which the crests were abbut 

 \ inch apart. 



The first photograph gives a general view of the tree ; the 

 second represents the lower side of the bent portion of the 



Fig. 2. 



trunk, and shows very clearly the rending effect of the lightning 

 on a fibrous tissue. 



The photographs were taken about a fortnight after the tree 

 was struck, during which time there had been much wind and 

 rain. Percy E. Spielmann. 



Adaptation of Instinct in a Trap-door Spider. 



The following extract from the Sydney Bulletin, January 12, 

 sent to me by a correspondent in Western Australia, re- 

 counts an observation sufficiently interesting, I think, to be 

 reprinted and put on permanent record in a scientific periodi- 

 cal : — " A friend of mine noticed near his camp a trap-door 

 spider run in front of him and pop into its hole, pulling the ' lid ' 

 down as it disappeared. The lid seemed so neat and perfect a 

 circle that the man stooped to examine it, and found, to his 

 astonishment, that it was a sixpence ! There was nothing but 

 silk thread covering the top of the coin, but underneath mud 

 and silk thread were coated on and shaped convex (as usual). 

 The coin had probably been swept out of the tent with rubbish." 

 As is well known, the doors of trap-door spiders' burrows are 

 typically made of flattened pellets of earth stuck together with 

 silk or other adhesive material. The unique behaviour of the 

 spider in question showed no little discrimination on her part 

 touching the suitability as to size, shape and weight of the 

 object selected to fulfil the purpose for which the sixpence was 

 used. R. L PococK. 



, March 6. 



Protective Markings in Cats. 



It will probably appear to many — as it does to myself — 

 that the development of a protective mechanism in a domestic 

 animal is not likely, and for several reasons — such as the short- 

 ness of time at the disposal of the race, and, of course, to their 

 large independence of stress of circumstances. Still it may be 

 admitted that the domestic cat bears its subjugation to man 

 more lightly than many of the other creatures which he has 

 tamed. The particular mark above the eye to which your 

 correspondent refers (p. 441) has also been pointed out by Mr. 

 Wallace in the dog. It may interest those of your readers 

 who are not aware of the fact to learn that the tiger has a 

 largish and very bright white spot upon the back of the ear. 

 When the ears are directed forwards this spot is exceedingly 

 conspicuous from in front (as any one may verify upon the 

 fine painof tigers now in these gardens) ; and, in the dimness 

 of a cave or a thicket, might conceivably produce an impres- 

 sion of alertness when the animal was really sleeping. 



Zoological Society's Gardens. Frank E. Beddard. 



