Jan. 19, 1 88 3] 



NATURE 



273 



ment. It is thus impossible to discuss the proper vahie of P^, as 

 Prof. Harkness wishes to do, without raising the question of 

 fallible observations. If it is raised, the method of treatment 

 by least squares follows. 



Prof. Harkness tried to show that, although the second term 

 which I introduced brought the approximate value of P^ nearer 

 to that given by the ordinary formula, it removed it further 

 from another value which he regarded as the standard. I venture 

 to think that I have justified my position by showing that the 

 introduction of P,, is useless unless the equations are regarded as 

 fallible ; that the ordinary value is that given by least squares, 

 and that the standards proposed by Prof. Harkness are founded 

 on assumptions which have no theoretical basis. 



In conclusion I may perhaps be allowed to make two remarks, 

 one of which would, I think, from the point of view assumed by 

 Prof. Harkness have strengthened his case. In the first place he 

 is wrong in saying that the ordinary value of P^ lies between P 

 and Pj. It is smaller than both of them if A is >Ai. 



In the next place I may point out that by treating a number of 

 fallible expressions of the lype of equations (i) and (2) by the 

 meth;id of least squares, a general value of L could be found 

 without the introduction of the small theoretical errors which 

 have caused this correspondence. There is however little doubt 

 that by the introduction of P„ we obtain a more convenient and 

 practically no less accurate method of dealing with the observa- 

 tions. Arthur \V. Rucker. 



Science Schools, South Kensington, January 10. 



The Mist-Bow. 



In a letter to the Turns of January 12, Prof. Tyndall calls 

 attention to a white mist-bow, which he has seen on one or 

 two occasions, and mentions its rarity of occurrence. It may 

 therefore be of interest to record that I witnessed a similar 

 plienomenon on January 9 last. My point of view was an elevated 

 band-stand at the head of Weymjuth Pier; the time il a.m. 

 The air, as on the occasions mentioned by Prof. Tyndall, 

 "swarmed with minute aqueous particles," i.e. was toggy, and 

 on looking away from the sun, which was shining weakly, I saw 

 a well-defined white bow cast upon the mist. The bow ap- 

 peared to be about 60 feet distant. My point of view being 

 high, a full semicircle was visible. It was, as maybe imagined, 

 a beautiful and graceful object. Albert Bonus. 



St. Leonards, Exeter, January 13. 



In reference to Dr. Tyndall's letter in the Times of Thursday 

 last upon the ullao as observe I by hiai, I be^ to call your at- 

 tention to my paper read before the Stockport Society ot 

 Naturalists upon the same subject (see pp. ii and 35). Not 

 having seen the phenomenon described before, I ventured to 

 call it the dew-bow. THOMAS Kay. 



Moorfield, Stockport, January 14. 



The c'liricter an J persistence of the recent fog have been so 

 exceptional that perhaps you may deem the following observa- 

 tions on it worthy a record in Nature. 



I was staying in Mid-Devon at a place in the valley of the 

 River Taw, some 10 miles north of Dartmoor. On Monday, the 

 9th instant, we were enveloped in a dense, damp, white fog, a 

 rare occurrence in that part of the country. Surmising that the 

 fog had no great vertical thickness, I sallied forth in the after- 

 noon to mount a hill immediately to the eastward. At a slight 

 elevation the sun was already making his appearance, and as I 

 continued my ascent, and the fog became more and more thin, I 

 saw before me on the then pale blue sky a beautiful white bow, 

 similar to the rainbow, only broader and without colour. When 

 the top of the hill was reached, the fog and bow had disappeared, 

 the sky was deep blue, and the sun shining with quite spring- 

 like warmth. 



The scene I now had around me was most enchanting. The 

 fo^ could be traced lying in the river valleys like arms of the 

 sea, with the bordering hills simulating cliffs, and here and 

 there an island appearing in the midst, whilst the distant Dart- 

 moor hills stood out calm in unbroken sunshine. No movement 

 of the air could be detected, but, below, the surface of the fof 

 seemed as if being rolled along by a wind from the east towards 

 the river valley. The white fog-bow is seldom seen, and I 

 imagine owes its absence of colour to the minuteness and close 

 proximity of the water globules, allowing the divided rays to 

 coalesce and so again form white light. C. O. Budd. 



Atmospheric Effects at Sunset. 

 On Sunday, January 8, upon leaving the house at half-past four 

 in the afternoon, I observed that the clouds were suffused with a 

 kind of pink or lurid coppery tinge, a sort of angry sunset tint 

 spread over the whole sky. The clouds were of the stratus type 

 which is common in a winter anticyclone, but were moving or 

 rather driving with a swiftness quite unusual under such conditions. 

 The barometer was very high and rising rapidly ; but during 

 the afternoon there were several violent and noisy gusts of wind 

 almost amounting to squalls, though during the greater part of 

 the day the atmosphere was still almost to stagnation. The air 

 was mild and intensely humid, and everything was dripping with 

 moisture. In fact the weather was in many particulars the 

 opposite of what we expect during the prevalence of an anti- 

 cyclone. The diffused sunset effects were quite unlike anything I 

 ever remember to have witnessed before. The gas-lamps had 

 just been lit, and the flames not only appeared of a greenish tint, 

 but seemed to be inclosed in green glass. Several persons 

 stopped me in the street and inquired what it all meant, and one 

 acquaintance said, " What is going to happen ?" In the green 

 tint of the gas there is, of course, some suggestion of a colour 

 complementary to the strange red glow which seemed to pervade 

 the atmosphere. But in the absence of all, even the most rudi- 

 mentary, knowledge of the subject, I should be glad if you or 

 some of your readers can explain the cause to me and to others 

 who witnessed the unaccustomed phenomenon. 



Charles Croft. 

 ; Prestwich, near Manchester, January 9. 



' Newton's " Principia." 



It may perhaps interest your readers to know that the 200th 

 anniversary of the publication of Newton's "Principia" was 

 salemnly celebrated on December 20 (old style) by a united meet- 

 ing of two learned Societies of Mo>cow — the Imperial Society of 

 Friends of Natural Knowledge, and the Mathematical Society. 

 Prof. Mendeleeff, of St. Petersburg, was Honorary President. 

 Prof. Stoletow (President of the Physical Section in the first- 

 named Society) presented a sketch of Newton's life, and spoke 

 on his optical discoveries; Prof. Zinger (President of the 

 Mathematical Society) treated Newton's mathemitical work; 

 Prof. Joukowski pointed out his merits as founder of rational 

 dynamics ; and Prof. Ceraski exhibited the creation of celestial 

 mechanics by Newton. The large hall of the Polytechnic 

 Museum, where the meeting took place, was attended by the 

 elite of the city. The lectures were illustrated by some 

 optical experiments with electric light and some lantern-slides 

 relative to Newton's biography. A. Stoletow. 



University of Moscow, December 2£, 1887 

 (January 2, 1888). 



Meteors. 



In the moonlight on the evening of January 2, at loh. 58m., 

 a fine meteor, equal in brightness to Jupiter, was observed by 

 Mr. D. Booth at Leeds, and by myself at Bristol. As seen 

 from Leeds, the meteor passed from Musca to the head of Cetus, 

 and terminated its course about 3° east of a Ceti. It moved 

 rather quickly, leaving a long thin train. The fore-part of the 

 nucleus was tinted with red, but the train was yellow. At the 

 finish the motion became slower. At Bristol the meteor was 

 first seen when about 6" S.E. of C Draconis, and it travelled 

 some 8" in the direction of /S Cephei. Colour yellow, motion 

 very slow. The course was evidently much foreshortened close 

 to its radiant. 



Comparing the two paths, it will be found that they inter- 

 sect each other at 250" -h 57', so that the meteor was not a 

 member of the January Quadrantids, which attain a maximum 

 on January 2, but belonged to a neighbouring shower of Dra- 

 conids, which, between January 14 and 19, I have previously 

 observed at 253" -f 56°. The meteor appears to have been 

 observed earlier in its flight at Bristol than at Leeds, for at the 

 latter place the observer was watching the southern sky, and 

 only caught the later part of the course. From a mean of the 

 two observations the height at commencement was 98 miles 

 above a point west of Appleby, Westmoreland, and the end 

 occurred at 60 miles above Chester. The earth-point was near 

 Tiverton, in Devonshire. The real length of path was 109 

 miles, and it was inclined at an angle of 20^" to the horizon. The 

 meteor was travelling in a direction from north to south, the 

 bearing of the radiant being N. 84° E. '-.- 



