546 



KNOWLEDGE & SCIENTIFIC NEWS. 



[September, igo6. 



the great southern continent of the Old World. One of the 

 latest workers on this fauna is Dr. R. Broom, Professor -A 

 Geology and Zoology at the Victoria College, Stellenboseh, 

 who has lately published a paper on these reptiles under the 

 serial heading of Science in South Africa. .Ml who are in- 

 terested in a very interesting subject should make a point 

 of consulting this e.xcellent little ri'svme. 



Freshwater Faunas. 



.\s was remarked, in connection with the " Broads," in 

 the last presidential address to the .Norfolk and Norwich 

 Naturalists' .Society, much work remains to be done before 

 we can consider our knowledge of the inhabitants of even 

 our own freshwaters in anything like a complete or satisfac- 

 tory condition. If this be the case with the freshwaters of 

 Great Britain it is, a fcrtiori, much more so with those of 

 the tropics. Naturalists should therefore be pleased to learn 

 that Dr. Nelson Annandale, Deputy Superintendent of the 

 Indian Museum, Calcutta, has commenced a systematic in- 

 vestigation of the freshwater faunas of India, the results of 

 which are in course of publication in the Journal of the 

 .Asiatic Society of Bengal. Although only seven parts of 

 this memoir have appeared — and these very short ones — Dr. 

 .Annandale has already been enabled to record certain dis- 

 coveries of very considerable interest. He has, for example, 

 obtained an aquatic cockroach {Epitampra), belonging to a 

 group previously known only from the Malay States and 

 15orneo. More interesting still is the discoverv of an aquatic 

 weevil, since no representative of this group of beetles with 

 habits of this nature has hitherto been known. This 

 weevil, which is not even g^enerically identified, feeds upon 

 a particular kind of water-plant ; and I^r. .Vnnandale has 

 fortunately been able to describe its complete life-history. 



British Biting Flies. 



In connection with insects, reference may be made to the 

 publication by the British Museum of a beautifullv illus- 

 trated monograph of the blood-sucking flies to be met with 

 in the British Islands ; mosquitoes and gnats, as well as 

 horse-flies, etc., being included in the work. The feature of 

 the work (for the text of which, Mr. E. .\. .Austen is respon- 

 sible) is the enlarged coloured figures of a considerable 

 proportion of the species. 



CORRESPONDENCE. 



To the Editors of '■ Knowledge & Scienth-ic News." 

 De.\k Si ks, — In your current issue Mr. Porter draws attention 

 to the fact that an image may, under certain circumstances, 

 be seen by converging light reflected from a concave mirror. 

 This is interesting, but the instance is not by any means an 

 isolated one. The image may also be seen with an ordinary 

 convex lens, which is. of course, theoretically similar to a 

 concave mirror. To observe this, place a lighted candle behind 

 the lens at a distance greater than the focal length, and view 

 from a point between the lens and the real image of the candle. 

 The observed image is erect, and is still visible when the eye 

 is drawn close up to the lens. It is, in fact, nothing more or 

 less than the ordinary image seen by all persons who wear 

 convex spectacles. 



The mirror phenomenon is brought into line with text-book 

 optics if we regard the mirror and the lens of the eye as 

 together forming an optical instrument which throws a real 

 image of the candle on the retina. 



Yours truly, 

 Sheffield University. Leonard Southerns 



.August t6, igo6. (Whit. Schol.). 



[The image referred to must, of course, be obtainable from 

 any optical system producing a real image by means of rays 

 of small convergence. The comparison with the ordinary use 

 of spectacles is, I think, rather misleading. Convex spectacles 

 for distant vision are employed when the wearer is able to 

 focus only convcixing pencils. One object of my note was to 

 indicate that the power of forming a tolerable image by means 

 of converging pencils is common to those who are not really 

 long sighted. For example, I am quite unable to accurately 

 focus the stars, but images formed as above are tolerably 

 good, I do not concur in the last paragraph of Mr. Southerns' 

 letter, because it fails to recognise that the images are iisually 

 imperfect. — A.W.P,] 



REVIEWS OF BOOKS. 



ASTRONOMY. 



A Compendium of Spherical Astronomy, with its applica- 

 tions to the determination and rctluction of positions of the 

 fixed stars, by Simon Newcomb (New York .and London : 

 .\Iacmillan Co., 1906; pp. .xv +444; 12s. 6d. net). — This is the 

 first of a projected series designed both for the student and 

 the investigator, suppljing the one with ;i condensed hand- 

 book which talci's very little account of branches of purely 

 theoretical interest, and the other with a vade mecum, con- 

 taining just those formulcB and data which are necessary 

 for the working out of jjractical applications by the shortest 

 or most convenient method, thus saving what is often the 

 most irksome part of his labour, which may be called 

 " sparring for a hold." Part I. contains such general pre- 

 liminaries as .Approximations, Interpolation, Method of 

 Least Squares, and Probable Error; Part II., Spherical 

 Co-ordinates, Conversion to DilTerent .Axes, Solar and 

 Sidereal Time, Parallax, .Aberration, Refraction, Precession, 

 and Nutation, having regard to the comparatively long 

 periods now covered in catalogue comparisons. This last 

 point is still more strongly emphasised in Part III., which 

 deals with the actual reduction of stellar observations for 

 epoch and apparent place, and also, of course, to the 

 meridian, and with the comparison of catalogues and deduc- 

 tion of proper motions. .A list of independent catalogues is 

 given at the end of Part III., and an appendix follows 

 giving tables for nearly every purpose referred to in the 

 volume, and constants and formulae in frequent use. 

 .Altogether a very valuable book, which we can confidently 

 recommend. 



BOTANY. 

 School Gardening (or Little Children, by Lucy R. Latter 

 (.Swan Sonnenschein and Co. ; 2s. 6d. net.) — .An excellent 

 little book, brimful of exactly the proper kind of informa- 

 tion recjuired by those whose duty it is to train children to 

 observe and draw deductions for themselves. The garden 

 proper is not the only thing utilized for the purpose of im- 

 parting information ; the various forces that enable a garden 

 to exist — light, heat, rain, wind, &c. — are also included, and 

 the effect of each in turn furnishes an object lesson, hence 

 the child is introduced unconsciously, and in the pleasantest 

 of ways, to the elements of botany, physics, zoology, and, 

 above all, the power of observation. 



The wisdom of teaching what must at some time be 

 unlearned is, perhaps, doubtful, and to a mind that is re- 

 ceiving lirst impressions, such terms as " seed-box," for 

 fruit, " dust spikes," for stamens, and " sticky-head," for 

 stigma, are not more explicit, neither more easily remem- 

 bered, than the proper names of these structures. 



PHOTOGRAPHY. 



The Hand Camera Companion and Guide. Edited by the Rev. 

 F. C. Lambert. M..A. (London : Hodder and Stougbton, 1906; 

 IS. nett. — On the title page Mr. Lambert appears as the author, 

 and presumably as these words are generally understood be 

 has been more of an author than an editor in preparing this 

 volume. Mr. Lambert is essentially a clear writer and well 

 understands the beginner's wants. In a series of beaded 

 paragraphs he discourses concisely on hand cameras and 

 their various parts, making negatives and printing from them, 

 and the application of the processes described to all sorts of 

 subjects. The page headings are carefully selected and there 

 is a good index, so that although the work is not divided into 

 chapters it is easy to find any required section. The volume 

 contains a great many practical hints and useful suggesticns 

 that are not often found in print, and is well worth study by 

 those who use, or are about to use, hand cameras. 



The Photographic Picture Post-Card. By E. J. W.^ll. F.R.P.S-, 

 and H.SnowdenWard, F.K.P.S. Magnesium Light Photography. 

 By F. J. Mortimer, F.K.F.S. (London: Dawbarn and Ward. 

 IS. net, each.) — Judging from the recent output of various pub- 

 lishers, the demand for small volumes dealing with just one sec- 

 tion of photographic work seems to be increasing. This method 

 of dispensing information, although not without its disadvan- 

 tages, enables the buyer to get what he wants as he wants it, 

 and oiten makes it possible for the publisher to secure a 



