70 



HARDWICKE'S SCIENCE-GOSSIP. 



caterpillar of this moth, but have a most vivid and 

 disagreeable recollection of having handled the 

 cocoons of the Vapourer {Orgyla antiqua), and 

 thereby encircled my neck with a ring cf 

 terribly-itching blisters, which became worse the 

 harder they were rubbed. I had, after handling 

 the cocoons, incautiously raised my hand to my 

 ueck, and the fingers being coated with the hairs 

 caused the mischief. I think there is but little 

 doubt that the effect is produced by the hairs. 

 Have the latter ever been microscopically examined, 

 and if so, do they present any difference in structure 

 from ordinary hairs? — W. H. Warner, Kingston. 



Erratum. — The heading of ray little article on 

 p. 33 should have been "A Nut-storing Bird," 

 instead of "A Nut-stowing Bird."— /T. E. IF. 



White Sparrow. — A. white variety of the 

 common Kouse Sparrow {Passer domesticiis) was 

 shot last November in this neighbourhood, but was 

 too mucii damaged for preservation. A remarkable 

 variety of the Robin [Enjthaca rubecula) was brought 

 to me some years back, in which the tail and the 

 greater part of the wings was of a buft' or cream 

 colour. I have also seen a starling {Sturiiv.s vulgaris) 

 which had been shot in Berkshire, which had the 

 head and neck, the wings and tail of the usual 

 starling colour, but the rest of the plumage was 

 cream-coloured. — IF. II. Warner, Kingston. 



Ophrys apifera in Herts. — There is another 

 station for 0. apifera in the neighbourhood of 

 Welwyn of a very similar character to Mr. Blow's. 

 It occurred a few years back in some plenty on the 

 bank which separates the Great Northern Eailnay 

 from the high road to London, immediately to the 

 south of Hatfield. This is on made ground, the 

 road and railway running side by side in parallel 

 cuttings, and the dividing ridge on which the plant 

 occurs having been, in addition, artificially raised to 

 shut out the trains. There is a record for the Bee 

 Orchis at HatSeid in Gerarde (quoted in "Flora, 

 Herts "), but Ido not know that it has been noticed 

 there since his day, and 1 have not had an 

 opportunity lately of ascertaining if it still exists. 

 Is not "rare" rattier too strong a term for Opirnjs 

 apifera — in South Britain, of course ? There are, 

 too, a good many localities recorded for Herts in 

 the published Elora of that county. — R. A. Prgor. 



Optics.— The peculiarity noted in " An Optical 

 Query " at p. 20 results from the construction of 

 tlie seat of vision : it is a defect of sight, one of 

 those "faults" that arise in the very nature of 

 things. We have no perception of light at the 

 point where the optic nerve enters the choroid, a 

 membrane that lines the eye internally, the coat 

 beiiig_ perforated or deficient at the point of junction. 

 This is shown by a conunon experiment. " if two 

 discs of white paper be fixed upon a wall at the 

 distance of two feet apart, and the observer with 

 the left eye closed gazes attentively at the left- 

 hand disc, slowly retreating, he will for a time 

 continue to see them both . . . wdien he has 

 reached a distance of about eighty inches from the 

 wall, the right-hand object will suddenly disappear 

 . . . till he has gained the distance of about one 

 hundred inches. During this period the spectrum 

 has been passing over the circular aperture in the 

 choroid through which the nerve enters." — Abridged 

 from the Penny Cyclop., vol. x. p. 141. The case 

 of " Interference of Light," cited at p. 20, is very 

 analogous to the polarization of light shown in the 



blue colour of the sky. This is the law of inter- 

 ference. "If two minute pencils of light, radiating 

 from two different luminous objects, meet at the 

 same point, equally distant from the luminous 

 objects, a greater intensity of light is produced 

 than by eith(;r pencil singly ; also, if the length of 

 one of the rays exceeds that of the other by some 

 certain difference, or by some multiple of that 

 difference, the intensity of the light thrown on the 

 point of junction is similarly augmented. But if 

 one ray is longer than the other, only to the amount 

 of half that difference, or some multiple of the half, 

 the two pencils will destroy each other, and a black 

 spot or fringe will be produced. The difference of 

 length required by the different coloured rays is 

 different. This mutual action of the rays, increas- 

 ing each other in one case, and destroying] each 

 other in the other case, is termed ' interference.' " 

 — Erom Maunder and Johnson's Scientific Treasury, 

 p. 3S2. Professor Tyndall considers the blue light 

 of the sky to be due to reflected light. " Let the 

 beam impinge obliquely upon a plane glass surface, 

 . . the ])ortion reflected will no longer have its 

 particles vibrating in all directions round it. By 

 the act of reflection, if it occur at the proper angle,* 

 the vibrations are all confined to a single plane, and 

 light thus circumstanced is called pla7ie polarized 

 light. A beam of light passing through ordinary 

 glass executes its vibrations . . . exactly as it 

 would do in air, or in ether-filled space." — Fort- 

 nightly Review, Feb. 1S69, p. 239. 



The Compass-flo-wer.— The plant inhabiting 

 our Western plains and called the Compass-plant, is 

 SiJphium laciniatmn. It is not, liowever, a " de- 

 licate" plant, as Father Felician says, but a large 

 coarse weed, from three to six feet high, with 

 leaves from twelve to thirty inclies long. The 

 lower and root-leaves are vertical, and present 

 their edges approximately north and south, from 

 whence it derives its name of " Compass-plant." 

 At the nineteenth meeting of the American Asso- 

 ciation for the Advancement of Science, at Troy, 

 N. Y., in August, 1870, Dr. Thomas Hill read a 

 paper on the Compass-plant, a short abstract of 

 which mav be found in the American Naturalist, 

 vol. iv. 1S70-71, p. 495. Dr. Hill slates that in a 

 journey from Omaha to Chicago, at three different 

 points, he noticed young plants of the Silphium 

 laciniatum, and estimated their bearings at 35", 7i>°, 

 and 90° ; he afterwards found the truejbearings were 

 31°, 78°, and 90°. Your correspondent will find a 

 discussion of the causes of this polarity in an 

 article by Mr. W. E. Whitney, in the American 

 Naturalist for 1871, vol. v. p. 1. The article con- 

 cludes as follows: — "But the observations here 

 recorded appear to show that the meridional 

 position of the edges of the leaf is to be explained 

 by the structure of the two surfaces, which being 

 identical, at least in the important respect of the 

 number of stomata, seek an equal exposure to the 

 light ; — the mean position of equal exposure, in 

 northern latitudes, being that in which the edges 

 are presented north and south, the latter to the 

 maximum, the former to the minimum of illumi- 

 nation." — Richard Bliss, jun., Cambridge, Mass, 

 U.S.A. 



Spiranthes ^stivalis. — I see the fact of 

 Spiranthes ccstivalis having been found during 

 the last few years questioned in the last issue of 



* The proper angle is 33°; will that suit the observer's 

 position with referenc to the window ? — A. H. , 



