Nov. 19, 1 8 74 J 



NATURE 



47 



Eiiiuburgl], in whose laboratory Mr. Wright practised with them, 

 of the first use of smokeless coal-gas flames in acoustical experi- 

 ments as not long anterior to the date named by Mr. Wright 

 as that of his practical experience of their use. But it must 

 be borne in mind that of all highly inflammable and intensely 

 heating gases next to hydrogen, the most easily procurable since 

 the general extension of the use of coal-gas, is an explosive mix- 

 ture of the latter gas with air ; and the experiments of Sir H. 

 Davy, in 1816, having demonstrated that such a mixture may be 

 prepared safely underneath wire-gauze and may be safely burned 

 aliove it, the use of the wire-gauze flame for laboratory heating 

 purposes, and also to illustrate very suitably the chemical har- 

 monicon, must have been a very e.arly suggestion. Its unwieldy 

 size and stentorian proportions for the latter purpose, however, 

 have not impossibly led to its comparative abandonment and 



«.— Conical and spiral mixing-tube coiled inside the foot, terminating at 

 the centre in a small chamber closed with wire-gauze at the top, at 

 the foot of the flame-tube. <^.— Conical wire-gauze cap, strengthened 

 by three wires to support the gas-tube, to protect the gas from ignition, 

 to keep off draughts, and to distribute the current of air to the gas 

 'junctwits all soldered), r.— Short flame-tube, closed at the bottom with 

 wire-gauze to prevent the flame from flashing back when the gas is 

 turned on or ofl'. Whole height about 2" in. Height of flame, ij in. or 

 2 in. Height of central bright ttame, exactly i in. 



disappearance from the scene of modern laboratory experiments, 

 and to its general replacement, in coal-gas illustrations of the 

 chemical harmonicon, by various modifications with difTerent 

 forms of jets, of the much more portable, convenient, and easily 

 adaptable Bunsen-burner. Thus a long- recognised and important 

 applicatioii of gauze-topped gas-burners in the student's scientific 

 practice might have fallen into oblivion, or into disuse and com- 

 parative neglect, if contemporaneous experiments like those of 

 Irvine, Barry, Govi, Geyer, Rijke, and it may safely be pro- 

 phesied of many other active fellow-workers in the same field of 

 discovery and research, diil not revive the discussion, and con- 

 tinue to develop the observation of these flames with multiplied 

 results that appear to be in perfect accordance with the principles, 

 and to furnish the most beautifully effective illustrations possible 

 of important properties of effluent gas-currenis, which would 

 perhaps othersvise escape detection. The laws of the flow of 

 escaping gas-jets, their powers of producing ventilation and 

 exhaustion, and, on the other hand, the means of providing for 

 their escape with as little waste of their energy as possible, are 

 questions of practical importance in so many useful industrial 

 applications, that they amply deserve the increased measure of 

 scientific attention which the beautiful succession of modern dis- 

 coveries of sensitive and sounding flames has been very materially 

 instrumental in attracting, and appears still further to be emi- 

 nently capable of directing towards them. 



Newcastle-on-Tyne, Oct. 19 A. S. IIerschel 



Insects and Colour in Flowers 



In his second letter (Nature, vol. xi. p. 28) Mr. Mott passes 

 to the discussion of the general question whether beauty is an 

 " object in nature." On that point my feeling is that our know- 



ledge IS as yet far too limited for us to presume to declare with 

 any confidence what is an object in nature. Still less should we 

 venture to assert what is not an object, and least of all have we 

 any right to affirm that beauty is not an oliject, when we see 

 developed, beauty of form, of colour, of sculpture and marking, 

 so constantly throughout the organic world, and liy such a gre.at 

 variety of means. _ Sometimes beauty of colour undoubtedly 

 exists when, so far"as we can see, it confers no benefit whatever 

 on its possessor. Mr. Darwin instances arterial blood and tlie 

 autumnal tints of leaves. More frequently it is accompanied by 

 some advantage, direct or indirect ; and the question is whether 

 in s!i(/i cases it has been acquired through the operation of sexual 

 or natural selection, more particularly whether in the case of 

 flowers the selection has been effected through the agency of 

 insects, which have favoured the most conspicuously coloured. 

 It remains with Mr. IWoU to show in what way the facts detailed 

 in his original letter (I hope he will pardon me for taking him 

 back to it) fail to harmonise with that doctrine. To my^mind 

 the fact that a cultivator, by carrying out a like selection, propa- 

 gating from plants which bear the largest and brightest, double 

 or showy sterile flowers, can produce like results, supports and 

 corroborates the doctrine rather than mihtates against it. Nor 

 can I see anything discordant in the fact that the colour of fruits 

 has been acquired through the medium of an entirely different 

 selecting agent. 



One circumstance appears to me to present some difliculty ; 

 and, although it is in no way connectecl with Mr. Mott's letter,' 

 I should like to mention it in the hope that others may be able 

 to supply a satisfactory explanation : it is the case of flowers 

 that are coloured on the outside, but white within. Where such 

 flowers from their position or form present to view principally 

 their exterior, as Tii/iftnirchiciim, this is an adaptation that can 

 be readily understood ; but some display mostly their interior, 

 and it is then difficidt to understand the acquirement of colour 

 uui.-idc only. I would instance Simethis bk-olor, Gypsophila ax- 

 tica. Daphne jas7ninea, and several species of white-rayed Com- 

 positfe. Bdlidiastrum michdii, for example, has frequently the 

 inner surface of the ray florets quite white, and when the flower 

 is open nothing else is seen; the colour on their outer surface 

 only becomes visible when they close over the disc, as in dull 

 and rainy weather. Thomas Comber 



Newton-Ie- Willows, Nov. 16 



With reference to this ([uestion, is cross-fertilisation so 

 desirable for the plant as is staled ? 



In this country, and I believe as a rule elsewhere, brilliant 

 flowers are produced by shrubs, climbing and heibaceous plants, 

 while the inflorescence of trees is comparatively inconspicuous. 

 Does it not seem probable that beauty of colour is gained at the 

 expense of strength, majesty, and longevity ? J. S. H. 



Droserae 



I FIND that during my absence from England many applica- 

 tions have been made for plants of the Droserx and Pinguiculse, 

 and from the replies which have been sent on receipt of the 

 plants they seem to have given satisfaction. Lately, however, 

 in consequence of the weather, there has been some difficulty ii'i 

 obtaining D. intermedia, but before this is printed in your 

 columns, all existing applications will be cleared off. 



I wish to add, tliat in winter these plants can scarcely be 

 expected to be as active as in spiing and summer, and observers 

 must wait patiently until spiing before they may hope to obtain 

 successful results fro-n their observations : it cannot be necessary, 

 I think, to fied carim'otOHS plants artificially during tlie winter'; 

 and a hot-house or conservatory cannot be absolutely necessary, 

 as they have no such advantages in their native wilds. 



G. II. Hopkins 



Suicide of Scorpions 



That scorpions do commit suicide, as described by your 

 correspondent last week, is a well-known fact. My grandfather 

 often related how he had seen these creatures, when surrounded 

 by a circle of glowing embers, make for the inner side of their 

 fiery prison, then deliberately move round the inside of the 

 circle, and when arrived at the exact spot from whicli they 

 started, turn back their tails and sting themselves to dei:h. 



Clyde Wharf, Nov. 16 M. L. 



