64 



KNOWLEDGE 



[Mabch 1, 1900. 



H cttcr g. 



[The Editors do not hold themselveB reeponflible for the opinioLs or 

 etatementa of correspon dents.] 



THE EARWIG AS A BENEFACTOR. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — Our commoa earwig (Foi-ficula auricularia) is 

 usually thought to be an unmitigated nuisance to the 

 gardener; it is coruidered destructive to fruit, it 

 damages dahlias, and is supposed to have a weakness 

 for exploring the cavities of the human ear. 



I^s scientific reputation is better; it was found to 

 be carnivorous, preferring dead insects to fruit or vege- 

 table food, and it has the amiable habit not hitherto 

 observed in other insects, of brooding over and rearing 

 its young. I have several times mounted the whole 

 insect as a slide for the microscope : one of these shows 

 the food in an undigested state, and I was surprised to 

 find on careful examination and comparison, that the 

 stomach was full of Aphides (green fly, plant lice), in 

 a more or less disintegrated condition. The identifica- 

 tion was placed beyond doubt by the discovei-y of several 

 of the characteristic tubes through which the Aphis 

 exudes the " honey dew." In another earwig I found 

 the scales of a Lepidopterous insect together with the 

 remains of Aphis in a, more digested condition. 



It is well known that the eai-wig is nocturnal in its 

 habits, and I would much like to know if any of your 

 readers have actually seen the insect commit the damage 

 it is usually credited with, or if the evidence is purely 

 circumstantial. In any case earwigs must do a certain 

 amount of good by the destruction of the plant lice, 

 and ought to have a measure of that tolerance extended 

 to them that is bestowed, or ought to be bestowed, on 

 the Syrphus fly, the Lady Bird (Coccinella Septem- 

 puncta), and the larvae of the Lacewing fly (Chrysopa), 

 on account of their habit of preying on these pests. 



South Hamjistead. Walter Wesche. 



SOME CURIOUS "lunar PHENOMENA. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — In last week's issue of " Nature " several 

 correspondents are quoted as having sent descriptions 

 of solar halos and parhelia obsers-ed from various parts 

 of Sussex and Surrey on Thui'sday, January 11th, be- 

 tween 9.30 and 11.30 a.m. The following account of an 

 unusual lunar phenomenon occurring on the same day 

 at 5 P.M. may prove interesting. I was driving home 

 from Beddgelert when the moon's peculiar appearance 

 attracted my notice. The moon was just at that moment 

 partly obscured by a thin cloud, but it was plainly 

 visible that surrounding and touching the disc there 

 was a distinct girdle about twice the moon's diameter in 

 breadth. When the cloud passed the sight was beautiful 

 beyond words. The well-illuminated disc had the usual 

 opaque markings — " the man in the moon "■ — almost 

 in high relief, while surrounding it there was a belt of 

 golden hue, which in its turn was encompassed with a 

 magnificent aureole of many colours, of which red, blue, 

 and violet predominated, the whole showing the moon 

 in the height of its glory. 



On the 15th inst. the moon presented a distinctly 

 green appearance, with a shai-p halo surrounding it at 

 an unusually great distance. 



In view of the exceptionally wet weather in this 

 district, ever since the 12th inst., it would be interesting 

 to know how far atmospheric influences go to account 

 for such appearances. 



Portmadoc. North Wales. Walter Williams, m.b. 

 Jauuaiy 24th, 1900. 



THE CONSTITUENTS OF THE SUN. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — With reference to the excellent article on the 

 above subject by Mr. A. Fowler, may I be permitted 

 to make a few remarks with special reference to Fig. 3 

 accompanying the article ? This pictm-e is entitled 

 ■' A solar comparison, showing how the presence of 

 carbon in the Sun is demonsti ated. (1) Carbon flutings 

 in electric arc, with iron impui-ity. (2) Solar spectrum." 



Now an examination of the two spectra pictured 

 here (which I presume are re-productions of photo- 

 graphs) by no means suggests to me an identity with 

 one another. I certainly see that three bright lines in 

 (1) coincide very completely with three dark ones in 

 (2), both as regai-ds appeai-ance and position; but these 

 three lines are apparently due to iron. None of the 

 other (dark) lines in (1) seem to have their counterpart 

 in (2). In fact I cannot see a single satisfactory co- 

 incidence. How then can the comparison of the two 

 spectra in question be said to demonstrate the presence 

 of cai-bon in the sun ? 



I always understood, especially in earlier days of 

 spectroscopy, that the exact coincidence of many bright 

 lines in a spectrum of a terrestrial substance, both in 

 thickness and in position, with a similar number of the 

 dark Fraunhofer lines constituted an enormously 

 favoui'able argument for the existence of that substance 

 in the Sun. 



Thus we read at p. 246 of Schellen's " Spectrum 

 Analysis" (translated by J. and C. Lassell) : — "A 

 glance at Fig. 91, in which the coincidence is shown of 

 more than sixty of Kirchoff s observed lines of iron, with 

 as many dark lines in various parts of the solaa- spectrum 

 between C and F, justifies the conclusion that those 

 dark lines are to be ascribed to the absorptive effect of 

 the vapour of iron present in the atmosphere of the 

 sun. The likelihood that such a coincidence of sixty 

 lines is a mere chance, bears a proportion to the suppo- 

 sition that these lines really make known the presence 

 of iron in the sun's atmosphere, according to the 

 doctrine of probabilities, 1 to 2/60, or in other words 

 in the ratio of 1 to 1,152,930,000,000,000,000." 



The figure referred to in this excerpt, is more or less 

 academical, being a woodcut. The upper portion re- 

 presents the solar spectrum on a small scale ; the lower 

 the spectrum of iron, bright lines on black background. 

 Each dark line of iron in the solai- sijecti-um is con- 

 tinued through the second spectrum as a bright line. 

 As there are 57 of these coincidences (not 65 as stated 

 under the plate), the effect to the eye is most remark- 

 ably convincing. 



Since the date of this work (1872) great advances 

 have been made in ths knowledge of the variations in 

 terrestrial spectra which can be produced under differ- 

 ent conditions in the laboratory, and the apparently 

 rigid and exact coincidences formerly laid down must 

 be considerably modified in the light of present know- 

 ledge. Without denying the existence of many terres- 

 trial elements in the sun, I would like as a layman and 

 one not vei-sed in the practical study of spectra in 

 powerful instruments to ask Mr. Fowler whether two 

 photographed spectra of an element and of the sun re- 

 spectively can be produced in juxtaposition so as to 

 show to the eye as complete and convincing a set of 

 coincidences as was given in the woodcut referred to, 

 which was evidently based on measurements only. Or 

 are the lines of any one element in the solar spectrum 

 so intermingled with those of other elements that it is 



