82 



NATURE 



[November 22, 1900 



for safety ; and, lastly, as to the financial return and the 

 disposal of profits when such exist. 



The second portion of the book is more directly con- 

 cerned with light railway development in England. A 

 useful chapter is concerned with an analysis of the Act 

 of 1896, while the special chapters on "The Question of 

 Gauge" and on "The Construction and Working of 

 Light Railways " are perhaps the most valuable in the 

 book. On the question of gauge it may be worth while 

 to quote Mr. Cole's conclusion, which is that for railways 

 making connection with main lines the standard gauge is 

 imperative, and that for smaller independent lines the 

 reduced gauge of thirty inches may be used. In this 

 connection we notice no reference to the Duke of West- 

 minster's narrow-gauge railway at Eaton Hall, though 

 this is, perhaps, the most instructive example of a small 

 and self-contained railway in the United Kingdom. 



The book contains a number of folding plates, showing 

 details of construction both of permanent way and of 

 rolling stock ; and a long appendix includes tables of 

 returns for many railways, both of standard and of light 

 construction, as well as the full text of the Act of 1896 

 and its schedules. 



Les Plaques sensibles au Champ electrostaiique. Par 

 V. Schaffers, S.J. Pp. xxxix -f 19. (Paris : A. 

 Hermann, Librairie Scientifique, 1900.) 



The phenomena treated of in this pamphlet are those 

 observed when an electric discharge from a powerful 

 Whimshurst was passed over the film of a photographic 

 plate between two metallic points which usually were both 

 m contact with the film. A great variety of films, con- 

 taining various metallic salts mixed with different emul- 

 sions, &c., besides those ordinarily used for photographic 

 purposes, were tried. 



The potential difference used was not enough to spark 

 across between the poles, and the changes produced in 

 the films are probably mainly due to the current through 

 the film, and not to the discharges through the air above 

 it. In some cases the marks produced on the plate were 

 approximately parallel to the lines of electrostatic force or 

 current stream lines through the film, and several plates are 

 given showing the effects obtained in such cases. A 

 considerable variety of peculiar and more or less in- 

 teresting appearances are clearly described, and possible 

 explanations of them discussed. Scarcely any variations 

 in the method of submitting the material to the action of 

 the discharge were tried, and the object of the experi- 

 menter seems to have been more to obtain a large variety 

 of peculiar appearances than to really elucidate the 

 nature of the actions taking place. The method of 

 obtaining pictures of the lines of force or current stream 

 lines between conductors on the plates is described in 

 detail, and such pictures as the author points out may be 

 useful for educational purposes in some cases. 



H. A. W. 



The Elements of Plane Trigonometry. By Prof. W. P. 



Durfee. Pp. vi-f-105. (Boston, U.S.A. : Ginn & Co., 



1900.) 

 There are a few novel points in this book. Logarithms 

 and their use in computations are dealt with in the first 

 chapter, and most of the exercises are of a character 

 which will lead the student to see that trigonometry has 

 a practical value. The second chapter deals with trigo- 

 nometrical ratios, and is followed by chapters on un- 

 limited Angles, reduction formula, the addition theorem, 

 relations between the sides of a triangle and the trigono- 

 metrical functions of its angles, and solution of triangles. 

 Logarithms are used in all the calculations. The course 

 of work in the book is suitable for elementary students 

 of trigonometry, and constitutes an introduction to the 

 theory of functions as illustrated by trigonometrical 

 ratios. 



NO. 1621, VOL. 63] 



LETTERS TO THE EDITOR. 



\The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.^ 



Autotomic Curves. 



Mr. Richmond's letter appears to be written under a mis- 

 apprehension. My objection to such phrases as '' non-singular 

 cubic curve," " non-singular curve of the «th order," arises from 

 the fact that a point of inflexion is just as much a singularity as 

 a node, and that it is therefore inaccurate and misleading to 

 describe such curves as non-singular. In fact, the only non- 

 singular curves which exist are conic sections ; all others are 

 singular. On the other hand, the word autotomic exactly ex- 

 presses the idea it is desired to convey ; and I have been in- 

 formed by several excellent Greek scholars that they do not 

 consider the phrase "an anautotomic curve" open to objection, 

 and that the alliteration may be frequently avoided by the use 

 of the words every or any instead of an. 



The terms sesecting and non-sesecting appear to be unobjec- 

 tionable from a literary point of view ; but with regard to un- 

 autototnic and nodeless there is a general consensus of opinion 

 amongst writers who are careful about their style against the 

 use of hybrid terms composed of words belonging to two 

 different languages. A. B. Basset. 



Fledborough Hall, Holyport, Berks, November 16. 



A Remarkable Dolphin. 



Dr. Way, the headmaster of Rossall School, has recently 

 forwarded to the Natural History Museum (for determination) 

 portions of a cetacean stranded at Rossall in September. These 

 portions include the skull, the imperfect flippers, the tail (in- 

 cluding the caudal vertebrae), and the back-fin. 



The skull and other bones leave no doubt that the animal is 

 the bottle-nosed dolphin (Tursiops tursio). In place, however, 

 of the ordinary "flukes" of a dolphin, the tail terminates in two 

 long, narrow lobes, of which one is very much longer than the 

 other ; and, were it not placed in a horizontal instead of a 

 vertical plane, it might well be mistaken for the tail of a thresher 

 shark. The larger lobe of the tail measures 5 feet 3 inches, 

 while the total length of the remainder of the creature was 10 

 feet. A similar abnormal elongation is noticeable in the case 

 of the back-fin, which is about twice as long as ordinary, and 

 proportionately slender. Externally, both the tail and the 

 back-fin are thickly coated with small sea-weeds and sertularians. 



Judging from the teeth, the animal appears to be very aged, 

 and the only conjecture I can make in regard to the tail and 

 back-fin is that their abnormal form is due to pathological 

 hypertrophy, perhaps induced by an injury. I should be glad to 

 hear of any other instances of analogous malformation among 

 cetaceans. R. Lydekker. 



British Museum (Natural History), Nov. 19. 



The Optics of Acuteness of Sight. 



Observations have been frequently made upon the remark- 

 able eyesight of certain uncivilised tribes. Travellers have told 

 us of guides who could see four of Jupiter's satellites with the 

 unaided eye ; and lately Sir Redvers Buller has declared that 

 the average Boer can see at least two miles further than the 

 British soldier. It is of some interest to consider whether this 

 superiority is due to a real change in the optical properties of 

 the eye, or merely to some special ability to interpret slight 

 differences of impression, which might be acquired by practice. 

 As we have as yet no data as to the constants of a Boer's eye, 

 we may raise the question whether such feats are optically 

 impossible for an Englishman's eye. 



The minimum visual angle is determined by the transverse 

 diameter {c) of a foveal retinal cone, and its distance (F"K") 

 from the second nodal point of the eye. We have — 



tan — = ^ „ 

 2 F"K" 

 and, where c = '002 mm., F'K" = IS'498 mm. 

 I o = 26'6i8" 



I In order that two points may be distinguished as such by the 



