Atigust 30, 1877] 



NA TURE 



361 



and properly arranged to become admirable educational aids. 

 In few, however, is there enough ma'erial to engage the whole 

 time and attention of an able man in taking care of it ; indeed 

 a single month devoted to each of the departments of zoology, 

 botany, geologv, and so forth, would suffice, and, in many cases, 

 more than suffice, to put each into working order to begin 

 with, and after the first arrangement it would be easy enough 

 to maintain the efficiency of each collection and to add what 

 fresh acquisitions might be made in the course of a week's visit 

 once a year. 



Let, then, an association of the younger workers in the various 

 branches of science be formed in London, under the direction of 

 a committee of well-known names, and let it offer to send out 

 every year for short intervals, to such museums as should be 

 ready to pay for them, botanists, zoologi-ts, geologists, and the 

 rest, to name and arrange their several collections ; each member 

 so dispatched would then visit several museums in succession, 

 confining his attention in each to the collection made in his own 

 subject, and each museum would be visited by several members, 

 one member for each of its essentially different collections. Thus 

 for a slight expense (payment on the piece-work system) a large 

 number of our Local Museums would be put under the curator- 

 ship of a group of specialists, and so be brought into efficient 

 and permanent working order. The idea is simply that of visiting 

 curatorships supplied on the principle of co-operation, and made 

 possible by the facilities for travelling afforded by our modem 

 railway system. 



It can scarcely be doubted that in the summer, when lectures 

 and lecturing are over, many scientific men might be found 

 willing and able to undertake the task. W. J. S. 



Rainbow Reflected from Water 



Mr. Crookes' interesting observation of the reflection ol a 

 rainbow — described in his letter in Nature, August 16 — is 

 easily reproduced, on a small scale, experimentally. 



I fixed a "spreader" to the nozzle of a garden-engine so as 

 to cause a shower of fine drops of water to spread in the sun- 

 shine. The segments of a bright primary rainbow and of a 

 rather subdued secondary one stood out well-defined against the 

 dark foliage of some trees, the remainders of the bows being 

 lost against bright objects and sky behind. 



At whatever point the bows were visible, I found that by 

 placing a mirror or blackened glass wetted so as to form a 

 surface of water, in place of the eye, and then observing from a 

 fresh point, the reflections of both bows could be very distinctly 

 seen at the same time that real bows were also visible. 



The reflected bows were always apparently smaller in diameter 

 than the real bows which were visible at the same time from the 

 same position. The reason of this is, I presume, that the bows 

 seen in the mirror are not the reflections of the bows visible, at 

 the same time to the eye, but of bows which the eye would .see 

 if it occupied the place of the mirror, or rather of that portion of 

 it which is observed. When, for instance, the mirror is one yard 

 below the level of the eye, the drops by which the bows are 

 formed that are reflected by the mirror, are necessarily about one 

 yard below the corresponding drops by which the direct bows 

 seen by the eye are formed ; in other words the direct bows are 

 one yard above the bows which are actually reflected. There- 

 fore, when both are cut by a common horizontal line formed by 

 the surface of the mirror, a reflected bow must be the more 

 shortened of the two and its diameter apparently reduced. 



I would suggest ihat this may be the explanation of the dis- 

 placement of the colours where the real and reflected bows met, 

 which Mr. Crookes observed. Robert Sabine 



Hampton Wick, August 20 



The Greenland Foehn 



Dans le dernier numero (406) de votre journal je vols 

 que vous m'avez fait I'honneur de donner un abstract d'un 

 petit travail sur le foehn du Groenland. Malheureusement le 

 rapporteur n'a pas bien compris le danois (ou le norwegien) en 

 quelques endroils, et je me permettrai de vous indiquer les 

 meprises suivantes comme les plus dangereuses. 



2ieme alinea. — " Dr. Pfaff has carried on ... . and these 

 show that the aver.ige temperature of February, 1S72, was 

 — S°7 C, and a\ Fibruary, 1S63 — 3i°'6," etc. Les deux mots, 

 " February," sont omis, ce qui fait croire que je parle de la 

 temperature moyenne de Tannee au lieu d'un mois. 



5leme alinea. — " These explanations go a great .... when 



atjacobshavn shortly before July, 9° C. of heat are recorded." 

 Au lieu de "July"j'ai dit " Christmas "; une tempeiature de 

 9° C. est normale en juillet. 



Aoilt 21 W. HOFFMEYER 



On the Supposed Action of Light on Combustion 



Ln answer to Mr. Watson's inquiry contained in your last 

 number, I may state that at the meeting of the British Asso- 

 ciation at Exeter, in 1S69, I read a paper unier the above title 

 (.See Phil. Mag. for September, 1869), in which some com- 

 parative experiments were made on candles burning in full sun- 

 shine and also in a darkened closet. This mode of experiment 

 was adopted because it allowed the results to be tested by 

 weighing. Candles of the same make were used and hard 

 sperm candles preferred as being less affected by variations of 

 temperature than composite. The candles were allowed to burn 

 during four hours. I give one result : — 



In the dark (temp. 81° F.) each candle lost 544 grains, or 

 136 grains per hour. 



In the light (temp. 84°) each candle lost 567 grains, or 142 

 grains per hour nearly. 



It is evident that in this case the increase of temperature 

 caused by the bright sunshine led to an increased consumption of 

 material, but the general result was that hght has no retarding 

 .influence on combustion. , C. TOMLINSON 



Highgate, August 25 



Evolution by Leaps 



With reference to an article entitled " Evolution by Leaps," 

 in your "Biological Notes" (Nature, vol. xvi. p. 208), I would 

 call attention to a fact which is not unknown to horticullurists, 

 that a hybrid sometimes proclaims its origin by producing — 

 even on the sama rachis — flowers and fruits, some of which 

 resemble one parent and some the other. 



Many a time 1 have plucked a branch of two or three feet in 

 length from a pear-tree growing in a village in Kent, which bore 

 at the proximal end pears of a certain size and description, 

 and on the terminal twigs pears smaller in size, of a different 

 flavour, and later in blooming and ripening. 



As this "sport" prevailed throughout the tree, which was 

 large and flourishing, there was no possibility of its being the 

 result of a direct graft. Paul Henry Stokoe 



lieddington Park 



Zygoena Filipendulse 



In July last I was breeding some Zygxna filipenduhe (six-spot 

 Burnet moth) from pupa- taken in a chalk-pit near Cambridge, 

 one of which was developed into a moth with five wings ; four 

 of these correspond to the normal wings in this species and are 

 perfect in every respect, as also are five of the legs. The sixth 

 leg (a hind leg) is absent, its place being filled up by the extra 

 wing, which springs from the exact point at which the missing 

 leg would naturally join the body. In appearance the extia 

 wing resembles the ordinary hind wing of the species, but is 

 only about half its usual size. It is of a yellowish-red tinge, and 

 not so thickly covered with scales as the other wini>s of the 

 insect. Of the sixth leg there is no external trace whatever, as 

 far as I can see ; in fact it would seem at first sight as if the leg 

 had, by some means or other, been transformed intu a wing. 



This moth is subject to a good deal of variation as regards the 

 size of the spots on the fore-winL's, two of which are occasionally 

 united ; also, in this particuUir locality, the red colour is replaced 

 by yellow in about I per cent, of the specimens. The chalk-|iit 

 to which I have alluded is scarcely an acre in extent, and as the 

 species does not seem to occur elsewhere in the immediate 

 neighbourhood, continuous interbreeding must have been going 

 on for a long time. 



I have never met with or heard of such a curiosity of morpho- 

 logy either in this or any other lepidopterous species before, but 

 some of your readers will doubtless be able to adduce other 

 instances of a similar nature. N. M. Richardson 



Clare College, Cambridge, August 21 



I BEG to enclose a photograph of a specimen of D.'osera 

 rotundi/olia found by me at the Lickey Hills on July I this year. 



