Feb. 12, 1880] 



NATURE 



347 



magnitude of a star, the light of which, if diffused over a circle 

 one minute of arc in diameter, would be equal in brightness to 

 that of the nebula. 



The star employed as a standard in the pre ent instance was 



Cygni. The comparisons were made upon three evenings, and 

 three observers took part in the measurements. The number of 

 determinations is six. If we assume the magnitude of a Cygni 

 to be V), as in the Durchmusttrung, that of the nebula is 4'6 

 on the system just explained. The average deviation of the 

 separate results is o - 4, and the probable error of the mean 02. 

 The scale of stellar magnitudes here adopted is that of Pogson, 

 in which the ratio of light corresponding to one magnitude is 

 that the logarithm of which is C4. Accordingly, it appears that 

 the brightness of o Cygni would be equal to that of the nebula, if 

 the light of the star were diluted over a circle 3'S in diameter. 



In the position angle 140°, the diameter of the nebula is about 

 11", and the diameter perpendicular to this is about 8". The 

 border of the nebula is not sharply defined, and the fainter light 

 around it is not very regularly distributed about its central 

 portions. In a smaller telescope it would probably look smaller 

 and more nearly circular. 



From the measured dimensions and brightness of this nebula, 

 its total light may be computed. The result is that, according 

 to the-e observations, we receive 500 times as much light from 

 a Cygni as from the nebula. Hence, regarding the nebula as a 



star, its magnitude may be expressed by 17 + 2 ~11, or 86. 



o"4 

 The magnitude assigned to it in the Durchmusttrung is 8-5. 



1 his close agreement must of cour.-e be regarded as accidental. 



Like most of the planetary nebulae observed here, this nebula 

 shows a faint continuous spectrum, not due to the light of the 

 sky, in addition to the lines denoting its gaseous character. This 

 continuous spectrum is largely due to the nucleus. 



Edward C. Pickering 



Cambridge, U.S., January 24 



Electricity of the Blowpipe' Flame 



Col. Ross's experiment on the above subject seemed of such 

 importance that I thought it advisable to repeat it, and it may be 

 of interest to some of your readers to hear of the result and of 

 the way in which my experiment was conducted. 



A compass in a closed box, to prevent the influence of air 

 currents, was placed close to a brass Herapath blowpipe, and 

 after the position of the needle was noted the gas was lighted 

 and air w as blown through the flame ; no deflection of the needle 

 was observed. As the compass is an old one and there was 

 probably some friction on the pivot, it was replaced by a piece 

 of magnetised watch-spring attached to a mirror, and suspended 

 in a glass case by a single silk fibre ; this apparatus being placed 

 on a stone slab, light from a lamp was reflected from the mirror 

 on to a screen. The arrangement was so delicate that the needle 

 was set in oscillation by the movement of the iron rod connecting 

 the blowpipe with the treadle ; so, to avoid any possible disturb-" 

 ing cau-e, the air was supplied by water pressure from a cot per 

 ler. When the jet was brought near the needle, the 

 flame being either in the magnetic meridian or at ri^ht angles to 

 it, not the least movement of the spot of light was perceived 

 although the screen was at a distance of about eight feet from 

 the mirror. 



As this result is so much at variance with that of Col. Ross it 

 would be interc ting to know exactly how his experiment was 

 performed. HERBERT M'Leod 



Cooper s Hill, February 4 



Triassic Footprints 



IN the Quarterly Journal of the Geological Society for 

 1. an interesting notice by Mr. Sollas, accom- 

 panied by a figure, of a set of footprints from the Triassic beds 

 of South Wales. Thee footprints Mr. Sollas says he has com- 

 pared with those of the emu taken in modeUing-clay ; and so 

 complete was the agreement that, other considerations out of 

 the question, he would not have felt much hesitation in de- 

 claring for the avian, and indeed ratitous, character of the 

 animal that produced them; but that because no remains of 

 bivds have occurred in the trias of the south-west of England, 

 while those of reptiles have, he refers them to either 7 

 saurus or Palceosaurus. 



I wish, therefore, to call attention to the fact that in these 



footprints there is shown that character of the crossing of one 

 leg over the other, and of turning out the toe, which persons 

 who have kept poultry may have noticed as conspicuous in the 

 walk of the domestic fowl ; that is to say, it places the foot, not 

 directly forward, but across the opposite leg, turning the toe well 

 out. Now this is distinctly shown in the relative positions of 

 these Triassic footprints. The first, or lowermost in the figure, 

 is that of the right foot, and the toes point to the right ; the 

 next (2) is that of the left foot, and crosses the median line of 

 the animal's path, and the toe of this (for only the middle one 

 remains unobliterated), points well to the left ; the third, being 

 that of the right foot, crosses the median line in the same way, 

 its toes pointing well to the right ; but the fourth (left), though 

 it thus crosses, has not the toe turned out, because the animal at 

 that point began to bend its course to the right hand. 



This track is thus, I venture to say, one made by the jaunty 

 step of the light-limbed bird, and not by the slouching stride 

 of the heavy-limbed dinosaur, even if this kind of reptile did 

 (as has not yet, notwithstanding its ornithic affinities, been 

 shown) walk erect, and exclusively on two legs ; and I am 

 induced to trouble you with these remarks, because just twenty 

 years ago (Quart. Jour. Geol. Sec, vol. xvi. p. 32S) I contended 

 that the existing Ka/it,r and other wingless (or, more accurately, 

 flightless) birds are the direct, and but little altered, descendants 

 of those which inhabited Trias ic continents in the southern hemi- 

 spere, of which one portion, that formed by Australia and New 

 Zealand, has been preserved in complete, and other portions, 

 such as South Africa and South America, in less complete 

 isolation since that remote period ; and it seems to me that the 

 footprints figured by Mr. Sollas furnish very satisfactory evidence 

 of the case. Searles V. Wood, Jun. 



Martlesham, near Woodbridge, January 30 



Rainfall in the Tropics 



My studies on the distribution of rain on the earth have oflen 

 caused me t j regret our want of know ledge about the quantity of 

 waier falling on the oceans, especially in the tropics. The 

 observations on the continents and large islands are very apt to 

 mislead us r.s to what takes place on the open sea. As there 

 seem to be very great difficulties about observing rain-gauges at sea, 

 I have thought it would be possible to gain some insight into the 

 matter by placing rain-gauges on the smallest and lowest islands 

 to be found on the ocean, the meteorological conditions of which 

 differ but very little, if at all, from those of the ocean. In the 

 Pacific such islands are to be found in plenty ; in the Atlantic I 

 would especially recommend the island of St. Paul J° N. and 

 29 J," W. ; in the Indian Ocean, the Southern Maledives, the 

 Chago«, and Keeling Islands, &c. 



The rain-gauges !or this purpose should be made of strong 

 metal, the lower part, instead of the ordinary glass measuring- 

 vessel, being also of metal. Such rain-gauges could be put on 

 islands, especially uninhabited, and taken up and the amount of 

 water fallen mea- tired after some months, or even a year cr 

 more. The measurement would be but a rough one, as the 

 evaporation could not be strictly accounted for, and we would 

 certainly know very little as to the distributii n of rain during the 

 year; but with all these drawbacks, even an approximate know- 

 ledge of the quantity of water falling in strictly oceanic climates, 

 far from the disturbing influence of land, would be very impor- 

 tant for meteor logy. Even a few figures as to the total annual 

 rainfall in parts of the ocean, which are for some months in- 

 cluded in the "doldrums," and those where the trade-winds 

 blow steadily the whole year, would very much increase our 

 knowledge, more than a great number of observations taken on 

 as islands, where local conditions modify the quantity 

 in the extreme. 



I refrain from further practical details, as these will be better 

 provided fur by B.-iii-h meteorologists and seamen, in ca e they 

 should accept my suggestion. A. Woeikof 



St. Petersburg, January 21 



Mountain Ranges 

 The reply which Mr. H. B. Medlicott has made to me in 

 Nature, vol. xxi. p. 301, seems only to obscure rather than set 

 aside or remove my objections. In the second sentence it is said 

 that I " take geologists to task for not making their descriptions 

 to fit in with my delineation of purely superficial features." But 

 my complaint was ba-ed, not on my delineation, but on a trigo- 

 nometrical survey ; and it was caused by a description — not of 



