278 



NAT ORE 



\yuly II, 1878 



and the whole of the electrical conducting materials are suitable 

 to its demonstrations. 



The one represents a patentable improvement, the other a 

 discovery too great and of too wide bearing for any one to be 

 justified in holding it by patent, and claiming as his own, that 

 which belongs to the world's domain. D. E. Hughes 



London, July 2 



Insects Corroborative of the Nativity of Certain Plants 



Whether certain plants are, or are not, natives of Britain 

 is a question that often exercises botanists, and any new evi- 

 dence on the subject is always acceptable. It has recently 

 occurred to me that a certain kind of evidence may be obtained 

 by studying the insects attached to such plants. The question 

 is one of interest not only to phyto- but also to zoo -geographers; 

 for if the species of plant to which an insect is restricted is 

 proved not to be indigenous then the insect cannot be indi- 

 genous either. If, on the other hand, the plant is only doubt- 

 fully an alien, and the insect is not one that might be easily 

 introduced, then the probability is that the plant is a true 

 native. 



The plant that has suggested this idea to me is the wild or 

 yellow balsam, Impaiieiis noU-me-tangere. This plant is re- 

 ported from twenty-seven counties or vice-counties, but in most 

 of these it seems to be admittedly an "introduction." Mr. 

 H. C. Watson, the indefatigable author of the "Cybele 

 Britannica," &c., seems to think that its claim to being indi- 

 genous is very slight, for he writes {" Topographical Botany," 

 part 2, p. 607) : — " If the Noli-me-tangere be really native 

 here it must be so very locally : say, in North Wales and West- 

 moreland." Sir J. D. Hooker (" Student's Flora," first edition, 

 p. 80) siys, "Probably wild in North Wales, Lancashire, and 

 Westmoreland ; " Prof. Babington (" Manual," seventh edition, 

 p. 72) does not mark it is an introduction, but Hooker and 

 Arnott ("British Flora") regarded it with doubt; finally 

 Hudson (" Flora Anglica," 1762, p. 332) thought it in his day 

 truly wild in Westmoreland. It is evident, therefore, that the 

 ImpatUns noli-me-tangere is looked upon with suspicion by 

 many of the present race of botanists, and probably rightly so 

 in many of the " stations." 



There are two species of Lepidoptera attached to this plant, 

 and, I believe, restricted to it. One of these — Lygris reticulata 

 — has been for a number of years known as a native of West- 

 moreland, where, on the banks of Windermere, it occurs very 

 rarely. Its connection with the Tmpatiens in this country was 

 not, however, known till very recently, when Mr. J. B. Hodg- 

 kinson, a well-known Yorkshire naturalist, traced it to its head- 

 quarters amongst the plant, where he also, still more recently, 

 found the other Lepidopteron — Penthina postremana — which is 

 attached to the balsam. Both of these insects are far from 

 common (though Lygris reticulata is, like its food-plant, widely 

 distributed — even as far as Siberia), and their occurrence in 

 Westmoreland seems to me conclusive that the Impatiens is 

 really indigenous there. 



As apparently opposed to my theory, it must not be forgotten 

 that there are several plants, certainly introduced into Britain, 

 which have insects attached and restricted to them. Amongst 

 others are the spruce-fir and the larch. On the spruce the 

 following insects occur : Eupithecia togata, Semasia ttanana, 

 Asthenia strobilella. Coccyx hercyniana, &c., and on the larch 

 Eupithecia lariciata, Boarmia crepuscularia, Spilonota lariciana, 

 Coleophora laticella, &c. But it must be remembered that the 

 sprace and larch are perennial trees (while the Impatiens is an 

 annual plant), and that they are frequently imported in the form 

 of young trees, or as undressed timber, and sent hither and 

 thither all over the country. Hence the insects attached to them 

 have many chances of being introduced, and of establishing 

 themselves where the conditions are favourable. 



It is possible that some of the insects I have last mentioned may 

 have transferred themselves from the native conifera; to the intro- 

 duced ones, but I do not think this is likely. A few species live 

 on the introduced as well as the native trees, as, for example, 

 Myelois abietella, upon scots-fir and spruce, and the rare beetle 

 Dendrophagus crenatus, upon scots-fir and larch, as I noticed 

 when investigating the natural history of Aberdeenshire some 

 years ago. 



It is desirable that all the "stations "in which there is any 

 doubt about the introduction of the Impatiens should be searched 

 tor the insects mentioned above, for it is not likely that they 



are confined to Westmoreland ; and should they be found in 

 any other locality, the probability is, it seems to me, that there 

 the plant is really indigenous. F. Buchanan White 



Perth, July 5 



Physical Science for Artists 



Some years ago, in Madeira, -we had been watching a glorious 

 sunset from the hills above Funchal ; and, on turning to go east- 

 ward, we saw the sky before us suffused with a bright rosy tint, 

 which ended abruptly beyond the Desertas, at some little dis- 

 tance above the horizon-line of the Atlantic. 



At first it did not occur to us what was the cold blue-grey 

 form that rose into the pink flush above, slowly losing its de- 

 finition of outline as it gradually grew higher. 



But this strange silhouette had so distinctly mountain outlines 

 that, almost at once, we recognised the fact that we were look- 

 ing at the shadow of Madeira cast by the setting sun on the 

 mist. 



This phenomenon may not be unusual, but I do not recollect 

 having seen it described ; and it is perhaps sufficiently different 

 from the phenomena described by Prof. Brucke and Mr. F. 

 Pollock to be worth recording. G. Hubbard 



Remarkable Form of Lightning 



I AM able to confirm the fact that lightning occasionally takes 

 the " punctuated " form described by Mr. Joule in Nature, 

 vol. xviii. p. 260. Some forty years ago, in a thunderstorm 

 which I had the good fortune to witness at Ampton, in Suffolk, 

 the lightning (with heavy rain) was almost incessant for half an 

 hour or more, and about a quarter of the flashes (speaking from 

 memory only) presented this unusual appearance. I have often 

 looked out for it since, but only once with success, and then it 

 only showed itself in a single flash out of many. On both occa- 

 sions the ' ' punctuated " flashes presented in general a curved or 

 sinuous line without sharp angles ; and two or three of them in 

 the first-mentioned storm appeared to my eye as closed curves, 

 one an almost perfect figure of 8 ; but their dazzling brightness 

 made it impossible to speak to this with certainty. 



London, July 8 E. J. LAWRENCE 



Microscopy. The Immersion Paraboloid 



The immersion paraboloid illuminator exhibited at the recent 

 soirSe of the Royal Society as designed by me, proves to have 

 been anticipated in principle and construction by Dr. John 

 Barker, of Dublin, from whom a paper on the subject will be 

 found in the Proceedings of the Royal Irish Academy for 1870. 



An immersion paraboloid illuminator was also described by 

 Mr. Wenham in the Transactions of the Royal Microscopical 

 Society for 1856. My paper on the subject appeared in the 

 Monthly Microscopical Journal for August, 1877, but that 

 journal being defunct, I ask you to allow me to credit these 

 gentlemen with a priority which, on perusing their papers, I find 

 to be due to them. I ought to add that, until the construction 

 by Messrs. Powell and Lealand of my illuminator, the device 

 had never come into practical use, and that, so far as I can 

 learn, no reference to it exists in any optician's catalogue or text- 

 book on the microscope. James Ebmunds 



8, Grafton Street, Piccadilly 



Review of Henfrey's Botany 



Allow me to correct an error which Mr. Bennett has made 

 in his review of "Henfrey's Elementary Course of Botany" 

 (Nature, vol. xviii. p. 217). He adds a note as follows : — 



" Evidently by an error of the press, the continued fraction of 

 which the most common angles of divergence are successive 



convergents, is given as - + - + -, instead of — , ^ , &c., 



i-f-i 

 a correction needful to render the sentence intelligible to the 

 student." 



My note (p. 44) is as follows : — 



" The mathematician will observe that these fractions are the 



successive convergents of the continued fraction - ^\ j^ "ij&c." 



I subjoined it for the sake of mathematical students only, who 

 would know what Mr. Bennett does not seem to be aware of, 

 that the method of writing the continued fraction I have adopted, 



