37^ 



NATURE 



[January i8, i 



bystflnclcr w-fs, h that th«? eye of the obiMTVpr shall be a* 

 nearly as prnrtirabU' in a Hne with the light and the n- 

 flrrtin^ eyeball. A pollccmnn, ior instanctr, may ((o hin 

 rounds nij^ht nfti^r night for years carrying his bull'jj-fye 

 :it thi' usual waiMbolt Ifvcl, and never have a notion of 

 thf numlM'rl»'«is pairs of rats' eyes which he would infallibly 

 st'v along thr area rails should he raise it to the Icvol of 

 his fncr. so as to look clostjly past his hand. There ! I 

 have let out my secret, and it only remains to tell what 

 I have seen in this way 



First, then, as to Bruno. It was my habit to stroll in 

 the garden with him of an evening, and I carried a bull's- 

 eye, by means of which 1 could always see where he was, 

 provided he was not moving away from me, or otiierwise 

 having both oycs hidden. .As to' the distance, the next 

 observation will give a fair idea. It was the way I 

 generally chose to show the sight to other people. Bruno's 

 greatest pleasure in life — ne.xt to accompanying me with a 

 gun— was to run after a ball, and after bringing it back 

 to gnaw it if not prevented. He would always prefer his 

 ball to his food if the former was thrown. His power of 

 scent was something remarkable. Hundreds of times have 

 I thrown his ball — wooden ones, which 1 turned for him 

 in the lathe as required, owing to his aforesaid destructive 

 practice, like full-sized croquet balls — when it was too dark 

 to see where he was, and he has never failed to find and 

 bring it, being guided as to general direction partly by my 

 .-iction and partly by the sound of the ball falling. Taking 

 advantage of this, I could always send him forth into the 

 darkness with the certainty that he would shortly be seen ' 

 by anyone holding a buU's-eye properly, returning in the 

 form of a pair of gig lamps bounding towards one in an 

 undulatory fashion most ludicrous to see. Under such 

 f.'uourable conditions fifty yards would be quite an easy 

 distance. 



1 wiU now pass on to cats. My experience of cats' eyes 

 is not so varied, but my belief is that, in relation to their 

 size, they reflect more light. I am sure they could be 

 seen, under similar conditions, at eighty yards, for I have 

 seen them brilliantly at half that distance. .At greater 

 distances there is not the same inducement for a cat to 

 turn her face in the right direction unless she has taken 

 refuge from a dog, say, in a tree. In such cases I have 

 had good opportunities. The greenish light from a cat's 

 ••yes— decided greenness at five yards at least — is easily 

 distinguishable from the redness which is so noticeable in 

 that from a dog's. 



The next experience I shall mention relates to sheep. I 

 was completely deceived the first time I saw the light in 

 sheep's eyes. .A flock had been let into the field adjoining 

 my evening walk without my knowledge, and there had 

 not been any there for, maybe, a fortnight. Moreover, it 

 was in the early days of my discovery of this amusement, 

 and I had not anticipated its range. However that may 

 be, the appearance of a numbt-r of lights, moving and 

 stationary, some down in a hollow, all more or less faint 

 and shimmering, gave me quite a turn ; for I have never 

 myself seen natural lights of this sort such as we hear of. 

 I believe I solved the riddle by getting over the fence — 

 after ascertaining that the phenomenon was connected, in 

 the aforesaid essential way, with the position of my lantern 

 — and studying it atnbulando, thereby learning, inter alia, 

 that sheep's eyes can be seen singly if the beast is walk- 

 ing past, and, of course, equally well, or even better, as 

 a pair if it is facing you. They are certainly visible at 

 fifty or sixty yards' distance with the light of an ordinary 

 bull's-eye as source. 



I have also seen rabbits' eyes, in the same way, 

 sufficiently well to speak positively, but not often enough 

 or under favourable enough conditions to describe 

 precisely. The light was certainly feebly seen ,at about 

 twenty yards. 



I have not seen the like satisfactorily in horses myself, 

 but others have seen it. 



Lastly, I have failed to »< any iran^ of it in human 

 eyes, nor have I heard of anyone else doing so. 



J. Herscuei.. 



1 1 am lold that readers not in the habit of using such lanterns, naUiral'y 

 suppose that the iffg^'s ivkoie form would be seen by its light. 1 he fact i<, 

 however, that even a strong light of this kind shows obiecis very feebly at 

 more than i«n yards, unless of a light colour. Practically the dQ£ is not 

 seen at all till quite cKise. 



The Weather of 1911. 



my letter on the above «ubj' ■ 

 January w) had Ix-en posted, it occurred to i; 

 gate to what extent temperature deviations 

 op|K>!,ite to those in England, and for tli! 

 compared the annual mean temperatures at .Al' - > 

 Cairo) with those for Kngland S.W. and Sou 11 

 (Weekly Weather Report, 1908, p. 42*)). This district v 

 iw-lected because Dr. W. N. Shaw, F.R.S. (Natubk, n 

 Ixxiii., 1905, p. 175), had already compared rainfall in i 

 region with wind velocity at St. Helena, and I had t- 

 pared the same rainfall with the volume of the Nile fio 

 (^uart. Journ. Roy. Met. Soc., xxxvi., 1910. p. 341). 



In the present case, a coefficient of correlat: 

 — 0-427 ±0097 was found for the annual mean temp< 

 tinres from 1877 to 1910. This looked promising, and 

 analysis by quarters was then undertaken with 

 result : — 



Temperatnre« *F. 

 S.W. England AUh-mua 



Mean S.D. Mean S.I> 

 1st quarter r= -0.724 + 0056 416 1-945 577 ^'^ ' 

 2nd „ -0-277 2:0108 51-6 1-252 7S 4 '^^ 



3rd ,, -0-165 + 0114 58-5 1-397 8o-8 1-31' 



4th ,, -o-544±oo83 462 1-557 652 1-47 



Year -0-427+0097 495 0944 698 0-92. 



The column headed S.D. gives the standard devintw.n f: 

 which, in conjunction with the means and ■ 

 correlation, the equations of regression can b- 



The connection between temperature in S.\V. 

 and Lower Egypt, as represented by .Abbassia, is 

 real in the first and last quarters, but only plm 

 the second. What the physical connection inay 

 more difiicult problem to solve. In the winter h... 

 Lower Egypt lies close to the axis of the ridge of 1 

 pressure which stretches across the .Atlantic, nortt 

 Africa, and Siberia, and the variations of weather 1 

 are dependent very largely on the position of this mi 

 It seems probable that the explanation will be found li 

 but the physical connection would still require invest 

 tion. In summer, on the other hand, Egypt lies on 

 slojje between the .Atlantic anticyclone and the In(i 

 monsoon depression, and probably receives its weot 

 from different regions from those which control went 

 in England. 



It is hoped to analyse the interrelations more fully 

 to investigate the position of the boundary between 

 regions of positive and negative correlation with S 

 England. J- L Crak 



Survey Department, Giza, Eg\-pt, January »i. 



NO. 2203, VOL. 88] 



Microscope Stands. 



I HAVE read with interest the article on the above ^ 

 ject in Nature of December 21 last. It would be intei 

 ing to hear if our expert workers agree with 

 conclusions arrived at. 



With regard to the centring of the condenser, in 1 

 many of the cheaper Continental stands does one find . 

 accurate means of centring whatever? Also, what grou: 

 are there for the assertion that the mechanical stages on 

 the Continental stands " as instruments of precision are 

 of a higher order than is obtained in the English models "? 

 Ihen, with reference to the mechanical draw-tube. Which 

 is cheaper, a mechanical draw-tube built with the sta-^'^ 

 to work with any objective, or a correction collar on > 

 objective? Is the latter arrangement really more accui 

 than the draw-tube properly used? 



I should also like to point out that the worker 

 easily keep sprung fittings in adjustment for an indefinite 

 IJeriod, but ground fittings would require the attention of 

 the repairer. Lastly, is there any evidence obtainable from 

 our most eminent workers with the microscope that the 

 English instrument has lost its former position as the 

 finest scientific instrument of its kind, and that that posi- 

 tion is now occupied by the product of a German house? 



John A. L. Sutcliffe. 



Boston Spa, January 5.* 



