NA TURE 



[July 4, 1901 



direction, and so to draw our attention away from the 

 serious dangers. In fact, we agree . . . that a man may 

 improve his reasoning habits by studying logic, but we 

 would lay rather more stress on the condition, ' if he has 

 the sense to know when formalities are out of place.' " 

 Mr. Sidgwick sketches the main points of his objections 

 to the scholastic logic in a way which can be easily fol- 

 lowed ; and in his last chapter, on " How Logic might 

 be Taught," he gives a succinct and simple explanation 

 of the main processes which are employed in reasonable 

 hinking. 



Holidays in Eastern Counties. Edited by Percy Lindley. 



Pp. 96. (London : 30 Fleet Street, E.C.) 

 It would be easy to select many places in which to spend 

 a restful holiday from those described and attractively 

 illustrated in this guide-book. The eastern counties pos- 

 sess many points of interest to students of nature and 

 archxology, and are worth exploration in the days of 

 leisure. 



LETTERS TO THE EDITOR. 

 {Thi Editor does not liold iiiinself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to retnrn, or to coi respond with the writers of, rejecied 

 ;iiaii!iscnpts intended for this or any other part of Nature. 

 No notice is tai;en of anonvmons conuniinications.'\ 

 A Vertical Light-beam through the Setting Sun. 

 The not very frequently observed appearance of a vertical 

 pillar of light through the sun when nearly setting was so very 

 remarkably distinct and bright this evening as to deserve, 

 perhaps, a particular description. I observed it in the Victoria 

 Park, near Hackney, in the north-eastern part of London, from 

 about 7h. 30m. to Sh. lom. p.m. The setting sun at the first 

 of those times was about 7^ or 8° above the horizon, and its 

 light was but little dimmed and tinged with yellow yet, by faint 

 ■cirro-stratus cloud-bands among which it was shining, which 

 ruled the western sky obliquely downwards towards a point' of 

 the horizon about 45" northwards from the sun. The light- 

 column then, when I first saw it, was yellow coloured, bright 

 and narrow at the base, but more diffused above, where it could 

 be traced up to a length of 5" or 6°, while its base rested upon, 

 or extended very little, if at all, below the sun. The summit 

 grew narrower and higher as the sun descended lower, while the 

 base became brighter and followed the sun down until, at about, 

 ten or fifteen minutes to 8, the sun was much dulled in light 

 and assumed an orange yellow colour in entering a bank of haze 

 about 5' from the horizon. Below that altitude the light- 

 column's base never descended ; but when at about 8 p.m. the 

 sun had acquired the magnificent appearance of a great crimson 

 disc, still about 2°, or some four of its diameters, clear from the 

 level park horizon, the tall column shone beautifully above it as 

 a perfectly straight, vertical, narrow streak of light about the 

 sun's apparent diameter in width and S° or 10" in length (from 

 about altitude 5° to altitude 15", and very faintly rather higher), 

 bright yellow at its base, but becoming insensibly whiter and 

 dimmer, without lateral diffusion till lost across the faint cloud- 

 streaks which seemed here and there just visibly to lengthen 

 it and very faintly extend it somewhat higher. It shortened 

 gradually, and died out at last about Sh. lom. p.m., soon 

 after the sun itself vanished in the haze before reaching the 

 horizon, but without changing the altitude, about 5°, of its base ; 

 and it retained to the last the straight, vertical appearance of 

 which many of the vast number of people enjoying the fine 

 evening in the extensive park were admiring watchers. I noticed 

 no horizontal belt of light through the sun, nor mock-suns at 

 their usual distances on its right and left hands, where the bands 

 of cirro-stratus yet extended far enough to have given rise to 

 them if they had consisted of cloud-materials of a fit and suit- 

 able description to produce them ; and nothing very notable, 

 except the vertical light-beam across the streaky clouds and the 

 sun's intensely red-coloured orb below it, seemed to be of very 

 marked meteorological significance in the beautiful display. 



It seems hardly doubtful that the vertical light-beam must 

 proceed in some way from passage of the sun's nearly level rays 

 through horizontal refracting surfaces, such as those, for example, 

 of thin, flat, hexagonal snow-crystals. A natural tendency which 



NO. 1653, VOL. 64] 



such floating crystals and collections of them into flat snow- 

 flakes possess, in fact, of remaining horizontal while falling 

 through perfectly still air, as flat leaves of paper, especially 

 symmetrically shaped ones, if started horizont.al on their 

 journeys also may be seen to do,' aftbrds fair grounds for an 

 assumption that the sun's slightly sloping rays are really dis- 

 persed into these observed vertical light-beams by passing 

 through the horizontal faces of such thin, flat, floating crystals. 

 In what further way the light is spread upwards and downwards 

 in passing through the thin transparent plates seems, indeed, to 

 be a rather more doubtful subject of conjecture ; but either want 

 of perfect parallelism of the plates' flat surfaces, perhaps through 

 partial melting, or refractions through the thin plates' bounding 

 faces which give them chisel-edges, supposing these edges to be 

 also slightly rounded oft by partial melting, would certainly 

 suffice, in the large proportion of a snow-cloud's floating crystals 

 which optical considerations show must always be suitably 

 oriented to produce refractions of the sun's rays upwards or 

 downwards in directions either vertical or as nearly vertical as 

 possible, to account for the columnar light-beam's well-defined 

 extension in a vertical direction. Yet for better insight into its 

 origin and surer proofs of the correctness of its theoretical ex- 

 planation, fresh attention to the features and meteorological cir- 

 cumstances of the beam's display when it is well developed 

 would certainly be desirable, and of great value to increase and 

 improve our knowledge of this rather rare and singular form of 

 halo, or occasional form of cloud illumination by the sun and 

 moon. .\ light north-west wind was blowing on the ground, 

 and the sky seemed to be dimmed by the faint streaks of cirro- 

 stratus only in that quarter of the horizon where the slender 

 beam of yellow light was visible ; but the air might easily be 

 quite calm and motionless aloft, in that thinly clouded region of 

 its very high upper strata. A. S. Herschei.. 



Observatory House, Slough, June 26. 



A New Method of using Tuning-forks in Chrono- 

 graphic Measurements. 



The tuning-fork, when used for making time traces in 

 chronographic work, is usually made to vibrate, by bowing with 

 a violin bow, or by percussion, or by rapidly removing a metal 

 block from between the two prongs, or by an electro-magnet 

 the circuit of which is interrupted by the fork itself. When 

 many details have to be attended to in an experiment, the first- 

 men tioned methods are inconvenient, and the last one, namely 

 the electrical, is not without an element of error. In order to 

 obtain the convenience of the electrical method without intro- 

 ducing the error due to the electrical driving of the fork, two 

 forks of the same period are used ; the fork which makes the 

 trace is furnished with an electromagnet, but no contact- 

 breaker, the current being controlled by the second fork, which 

 has a contact-breaker. This method of driving a chronographic 

 fork is well known. My new way of using this combination is 

 to cause the chronograph, during the short period during which 

 the records are made, to cut out entirely the electrical circuit 

 from the fork used to make the time trace and to close the 

 circuit again immediately after the records are made. By this 

 means the recording fork is not hampered with a contact- 

 breaker, nor is it subject to the influence due to the electro- 

 magnet, while its trace is being made on the moving surface of 

 the chronograph. After the time trace is made, the circuit is 

 again established, so that the vibration is maintained, and the 

 fork is ready for the next experiment. 



Trinity College, Oxford, June 28. F. J. Jervis-Smith. 



Long-tailed Japanese Fowls. 



With reference to Mr. J. T. Cunningham's letter on these 

 birds in Nature of June 13,1 should like to be allowed to point 

 out that the very interesting evidence he gives is yet not sufficient 

 to prove his point. The words of his correspondent do not 

 necessarily imply that he had personally witnessed the manipu- 

 lation part of the process adopted to secure extreme length of 



1 This is a rather surprising experiment to those who may have been 

 accustomed, as I have always been used hitherto, to see paper clippings, 

 when tossed up at random, pirouette like little windmills or teetotums in 

 falling through the air. But held by a corner for a moment, out of air- 

 draughts, horizontal, if the hand's support is withdrawn quickly, letting 

 them go at the same time without any impulse, squares, circles, hexagons, 

 or other small cuttings of flat paper will all be found to fall to the ground 

 from any height with very little oscillation, or even sometimes 

 throughout their fall quite horizontal. 



