366 



NATURE 



\March 9, 1876 



LETTERS TO THE EDITOR 



[ The Editor does not hold himself responsible for opiniom expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. ^ 



Professor von 



Siebold and the 

 England 



Freshwater Fishes of 



The object of the present letter is to appeal to naturalists 

 throughout the British islands to assist ^Prof. von Siebold — the 

 eminent zoologist of Munich — in his studies of the freshwater 

 fishes of Europe. Prof. Siebold is preparing a new edition of 

 his well-known work on that subject, and is exceedingly anxious 

 to obtain specimens of some of our British freshwater fishes to 

 compare with the specimens which he has collected from all parts 

 of Europe. In spite of various attempts, he has, I am very sorry 

 to have to say, failed to obtain specimens from English naturalists. 

 I am sure that this can be only owing to the fact that he has not 

 been able to make his wants known directly to those who could 

 help him. I have not myself been able to do much in supplying 

 the specimens of which he forwarded to me a list, but from the 

 Thames at Oxford have sent him Dace, Bleak, Pope, Miller's 

 Thumb, and Sticklebacks. The list to which I refer included 

 the Graining and the Azurine fishes which have been obtained 

 in or near Knowsley Park ; and I have received a kind assurance 

 from Lord Derby that efforts shall be made to procure speci- 

 mens for Prof. Siebold. Specimens of these and of the Powan, 

 the Pollan, the Gwynlad, and the Vendayce, are the chief de- 

 siderata which I am anxious to obtain for Prof. Siebold ; his list 

 also includes the Sharp-nosed and the Broad-nosed Eel. 



If any naturalist who possesses specimens of these fish which 

 he can spare for the purposes of scientific investigation, or who 

 can by reason of local opportunity obtain such specimens, will 

 forward them to me at University College, London, preserved 

 in spirit, I will transmit them to Prof. Siebold, taking care that 

 he shall know to whom he is indebted in each case. 



A more difficult task, I am afraid, is that of procuring speci- 

 mens of the Brine Shrimp, Artemia salina. Prof. Siebold has 

 made an extensive study of specimens of Artemia and allied 

 Branchiopoda from various European localities, and is anxious 

 to compare English specimens with those from other localities. 

 He wishes especially to obtain "gatherings" of these Crustacea 

 in order to determine the absence, presence, and relative abun- 

 dance of the male sex in different localities. Specimens from 

 Lymington or from Guernsey would be very welcome. 



I hope that through the columns of Nature I may succeed 

 in reaching those naturalists who, I am sure, are not few in 

 number, who will be willing to contribute material for the valu- 

 able researches which Prof. Siebold has so long been carrying 

 on. E. Ray Lankester 



March 5 



Seasonal Flower Distribution and the Radiometer 

 Vagaries 



Although apparently so dissimilar, there Is an intimate con- 

 nection between the seasonal order of colour in flowers and the 

 seeming erratic behaviour of certain radiometers. 



Whatever be the cause of the mechanical action of light which 

 is now exciting so much attention, the kind of light remaining the 

 same, the experiments show that different surfaces produce dis- 

 similar effects, the results with pith discs applying to pith only 

 and being different from those obtained with mica, which strictly 

 apply to mica alone. This is due in all probability to the differ^ 

 ence in inter- molecular conditions presented by the two sub- 

 stances. When these conditions are thoroughly understood and 

 a proper margin allowed for experimental errors, the observations 

 which seem now at variance will most likely be reconciled. To 

 acquire the needed knowledge, it is my humble opinion that 

 some modification of the present method will be required, 

 because many of the comparative experiments which have been 

 tried hitherto in the domain of radiant light and heat are open 

 to the objection that heterogeneous bodies having been dealt 

 with, a difference of chemical constitution has been introduced 

 for which no allowance could be made. To obviate this in the 

 present instance, and ascertain the result of such differences, 

 would it not be well to employ the following typical mode of 

 procedure : — 



In preparing the radiometer, let the discs be dipped into melted 



sulphur, or other convenient colour-changing body, and the com- 

 pleted apparatus inclosed in a jacket for the convenience of raising 

 the temperature. A series of observations made at the normal tem- 

 perature, when compared with a like series made at a high tem- 

 perature, would doubtless reveal many interesting facts. There 

 are many difhculties in the way which would take much experi- 

 ment to overcome. 



Now turn we to the flowers. The former question seems to 

 depend probably upon the reflection of light, and the latter on 

 absorption, the one being complementary to the other. I would 

 here call the attention of your readers to the behaviour of inor- 

 ganic coloured bodies when heated and to the laws of colour- 

 change given in Nature (vol. xiii. p. 298). There is here such 

 an identity of relations as nearly to preclude the possibility of 

 its being a mere coincidence, I shall speak more particularly 

 of this in another note in a few days. 



In reply to Mr. Rogers' query (p. 326), it may be remarked 

 that absorbed li^ht seems to be the active agent in vital work, e.g:, 

 it is the light absorbed by the retina which, as motion of some 

 kind, is transmitted along the optic nerve. This being the case, 

 it would seem highly probable that to exclude from a flower 

 such light as it reflects would not affect it at all, alihojgh of 

 course the only sure answer to such a query is experiment. 



Feb. 28 Wm. Ackroyd 



D-line Spectra 



With reference to Prof Stokes's courteous but rather theo- 

 retical explanation in Nature, vol. xiii. page 247 (which I 

 have been prevented from acknowledging before), I would ask 

 him or yourself for a practical explanation of the following sioaple 

 experiment ; — 



1. If platinum wire hi reddened from a constant source of 

 heat, as that applied to it by means of a blowpipe and a candle, 

 we find the D-line spectra indefinitely produced until incan- 

 descence takes place by additional heat, or, in other words, that 

 their permanency is in direct proportion to the bulk of the wire 

 used, and in inverse proportion to the amount of heat applied. 

 We can therefore, by using a thick platinum wire and the ordi- 

 nary flame of a blowpipe, produce D-line spectra as long as we 

 like, or as long as the fuel lasts. 



2. Now if this D-line producing flame be due to sodium, its 

 action for a long period upon a reagent so sensitive to sodiam as 

 is Boric Acid, ought to give a reaction by which the presence of 

 that alkali would be detected. Thus, if a pin's head speck of 

 pure cobalt oxide be heated by a blowpipe in a bead of pure 

 boric acid, it forms within it a black ball which the minutest trace 

 of any sodium salt partially dissipates, causing s.fink suffusion 

 round the ball. 



3. A boric acid bead fused upon the ring of a thin or ordinary 

 platinum wire, which has previously been made incandescent by 

 a blowpipe flame, i.e., from which the D-line producing property 

 has been previously removed, is clear, colourless, and refractive 

 as a diamond ; but if the same boric acid be fused upon a thick 

 platinum wire with the same degree of heat, the bead is opaline 

 and almost opaque ; and this phenomenon seems evidently and 

 only referable to the above-mentioned permanency of the D-line 

 spectra produced in the latter case. 



4. To settle this point, however, let us fuse a clear colourless 

 bead of boric acid on an ordinary platinum wire, and screw that 

 in a geometrical pen, along with, but a little behind {\}aaX. is, aiuay 

 from the source of heat) a thick platinum wire, so that the D-line 

 producing flame from the thick, hot wire, impinges constantly 

 and for some time upon the clear boric acid bead ; we find 

 opacity produced as in the former case. Now, supposing sodium 

 to he in this case, the producer of the D-line spectra, we ought 

 to have, in the opalised boric acid, a tangible result of the effect 

 of applying to it (according to Prof. Stokes) "free sodium," but, 

 on heating in it, as before, a speck of cobalt oxide, there is no 

 dissipation of any part of the resulting ball, nor the least pink 

 suffusion, but, on the contrary, a reaction, decided indeed, but 

 almost exactly the opposite of that caused by adding sodium to 

 the bead in any proportion. 



5. Let us now screw a platinum wire ring containing a boric 

 acid bead with a cobalt-borate ball inside, into a geometrical 

 pen behind another platinum ring containing a bead of some 

 soda salt, and heat both together with a blowpipe, so that the 

 orange flame from the latter impinges upon the former. Instead 

 of opalescence, similar to that caused by the orange flame from 

 the thick platinum (4), vre find the viscid boric acid made more 



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