August 2S, 1884] 



NA TURE 



407 



sun appears redder as it sinks towards the horizon, and loses 

 more of its blue rays in the thicker atmosphere. 



Gas and oil lights are richer in these penetrative rays than the 

 arc light, which is peculiarly rich in the blue rays easily ab- 

 sorbed. Hence a gas jet can be seen a long distance in a fog, 

 though, like the sun, it appears redder in tinge than usual. An 

 arc light, on the other hand, is not seen far, however penetrative 

 it may be in clear weather. I have often observed on London 

 Bridge, in a fog, that the arc lamps become of a blank white ; 

 the brilliant arc seems to disappear, and the carbon points, 

 slightly reddened, glow through the mist. The arc with its blue 

 rays is the part which suffers most, and hence the larger the 

 incandescent points in comparison, the likelier the light to 

 penetrate. The ordinary electric incandescent lamp has, ac- 

 cording to the late R. Sabine, 20 per cent, more orange rays 

 than daylight, a fact which may account for its greater penetra- 

 tive power than the arc ; but, owing to its cost, it is debarred 

 from lighthouse work. 



On the whole it would appear advisable to employ the spec- 

 troscope in the South Foreland experiments, in order to find out 

 what the absorptive action of mists is on arc, gas, and oil lights. 

 If it should turn out, as above indicated, that the arc fails in 

 penetration from lack of certain yellow, orange, and red rays, 

 it might be useful to try the effect of supplying the needful rays 

 by mixing certain salts with the carbons. J. Munro 



West Croydon 



The Cholera Germ 



The importance of our gaining clear ideas of the cause of 

 cholera as soon as possible prompts me to venture to suggest 

 the direction in which may be sought an explanation of the three 

 propositions in Nature (p. 26), and which " E. K." there says 

 "appear to me to be in hopeless contradiction." The proposi- 

 tions are, substantially, as follows: — (1) The comma-shaped 

 bacillus is the cause of cholera ; (2) the alimentary canal is the 

 exclusive organ of its entrance into the body ; (3) the comma- 

 shaped bacillus is killed by acid. 



The life of most plants is destroyed by passing through the 

 alimentary canal of animals or man, yet seeds of grasses, grains 

 of cereals, &c. , not infrequently pass through animals without 

 destruction, and afterwards germinate and reproduce their kind. 

 Seeds of small fruits sometimes pass uninjured through the human 

 body and through birds. Spores of bacilli are known to with- 

 stand treatment which is destructive of the bacilli themselves. 

 Unless the comma shaped bacillus is exceptional in not forming 

 such spores, it seems to me that the three foregoing propositions 

 may not only be thus explained, but that the} - may soon supply 

 an explanation of what has been long waiting explanation, 

 namely, the fact that the dejections of cholera patients are not 

 often, if ever, found infectious when first voided, but soon be- 

 come infectious. This accords perfectly with the three proposi- 

 tions if we suppose that the comma-shaped bacillus, soon after 

 being voided in the dejections, forms spores which are capable 

 of resisting the acids of the stomach. It seems very important to 

 have this point investigated. To plead for such investigation, 

 by whoever has opportunity, is a main object of this letter. 



The many instances of the outbreak of cholera in this country 

 (U.S.A.) immediately after infected baggage has been un- 

 packed, might then receive easy explanation ; the spores, being 

 inhaled with the breath, would be likely to lodge in the posterior 

 nares and pharynx, be swallowed, passed through the stomach, 

 and in the nutritive alkaline fluids of the intestines find a con- 

 genial soil in which to germinate, forming comma-shaped bacilli 

 giving off their poisonous by-product which seems to have such 

 baneful influence on the human nervous system. 



Lansing, Michigan, August 8 Henry B. Baker 



School Museums 



Dr. Gladstone do:s not allude to botanical specimens in 

 his communication to Nature last week (p. 384), but these can 

 forma very interesting addition. In my father's parish school of 

 Hitcham, he had a long row of phials fixed against the wall of 

 the class-room, with the name of every plant of the parish 

 attached below. These were kept constantly supplied by the 

 children all through the summer. Whoever first brought any 

 species had a small reward. The School Herbarium was entirely 

 made by the children ; and for the last twenty-five years I have 

 used for teaching purposes specimens dried, mounted, and 



labelled by the children of Hitcham School. Should any one 

 desire further details on the subject of botany in schools, I shall 

 be very glad to communicate with such. 



Drayton House, Ealing George Henslow 



The circulating loan collections of natural history speci- 

 mens, referred to by Dr. Gladstone in Iris letter on this subject 

 as being established at Liverpool, have been provided and 

 organised not by the School Board but by the Free Library and 

 Museum Committee of the Corporation. They owe their origin 

 almost entirely to the Rev. H. H. Higgins, chairman of the 

 Museum Sub-Committee, and their great value is due to the 

 close personal attention which that gentleman and the Curator 

 of the Museum (Mr. T. J. Moore) have bestowed on them. The 

 specimens included in the collections are not only typical, but 

 are of excellent quality, and cannot fail to arouse the interest of 

 the children before whom they are brought. So far as the ex- 

 periment has already gone it has proved very successful, and 

 deserves to be widely known. 



Having had the pleasure of bringing the matter of these col- 

 lections forward in the discussion on Dr. Jex-Blake's paper at 

 the Educational Conference, I should be glad if you would allow 

 me to make this correction as to their origin. 



21, Verulam Street, Liverpool, Aug. 25 W. Hewitt 



The Permanency of Continents 

 As a small contribution to this theory, the Cornish beaches 

 may furnish a quota. They are entirely composed of finely com- 

 minuted shells, with a small admixture of fragments of Bryozoa, 

 spines of minute Echinoderms, and occasional mica flakes. Such 

 sandy beaches occur in small bays, and if subjected to meta- 

 morphic action would form lenticular masses of limestone inter- 

 calated between the strata deposited above and below them. 

 Hence such occurrences of limestone might well indicate such a 

 littoral origin as is here displayed. 



St. Ives George Henslow 



Carnivorous Wasps 



I once witnessed a somewhat similar feat to that mentioned 

 by "F. N." (p. 385). It was at a wayside inn in the Eifel. 

 The tablecloth was covered with flies. The window was closed 

 excepting one small corner at the top. A wasp entered, came 

 direct to the table, but instead of attacking some stewed'fruit 

 thereupon, instantly seized a fly, bore it off, and after whirling 

 round with it, made straight for the small means of exit and 

 vanished. 



One evening when at College a small beetle was flying round 

 and round, but at some height over the lamp. A spider on the 

 ceiling watching his opportunity, suddenly dropped upon it and 

 caught it flying! He then ran up with it and began winding a 

 belt of silk round its body. However the beetle ultimately 

 managed to slip its meshes and escaped. 



George Henslow 



In reply to your correspondent " F. N.," I would say that, 

 while I do not recollect to have seen wasps, under natural condi- 

 tions and in the open air, attacking flies, I have frequently seen a 

 wasp, when shut up in a room, or supposing himself to be so 

 (for wasps are very stupid in finding their way out of a room), 

 attack and partially devour the common house-fly. I yesterday 

 witnessed an instance of cannibalism on the ^part of the wasp. 

 One of my drawing-room windows was closed, and on this seven 

 or eight wasps were engaged in a fruitless struggle against the 

 irritating and inexplicable glass, instead of escaping, as they 

 might have done, through the other windows, which were open, 

 One of them, more languid and weary than the rest, was 

 crawling slowly up and down near the corner of the pane. Some 

 minutes afterwards, looking up from my book, I noticed two of 

 the other wasps engaged in furiously attacking this individual. 

 After a few seconds, one of the opponents, perhaps endowed 

 with higher moral susceptibilities than the other, flew away. 

 The other seized upon the thorax of the now moribund wasp, and, 

 after a few moments, began devouring him. I watched the pro- 

 cess for a minute or two, and then the cover of a book put an 

 end to the existence of the cannibal and of his prey. 



A day without food reduces a wasp to a state of famine, and 

 it might be easily ascertained whether he does not commonly, 



