Oct. 1 8, 1888] 



NATURE 



603 



The apex of the earth's way is always 90 of longitude behind 

 the sun. 



Having, then, this general view of the movement of the earth 

 in her orbit, we are in a position to discuss Mr. Bompas's argu- 

 ment, and we cannot do better than use the explanation given 

 by Prof. Pritchar 1 to the Royal Astronomical Society in 1864, 1 

 which really possesses an historical interest. 



"Our object is to show that this hypothetical uniformity of dis- 

 tribution, combined with the direction and amount of the earth's 

 motion, will have a very sensible effect on the number of meteors 

 actually visible at a given place, at a given hour of the night, as 

 explained (in a somewhat different way) by Mr. Bompas [and at 

 a given season of the year, as extended by Mr. Herschel]. 



"For the purpose of illustration, suppose H o R (Fig. 11) to 

 represent a flat umbrella, of which N o is the stick ; suppose, 

 also, rain to fall upon it equally, and in all directions : then, if 

 the umbrella be at rest, as much rain will fall upon its front, 

 looking from z, as on its back, from N. 



" But now suppose the umbrella itself has a motion from o to 

 Ein a given time, and, for the simplicity of first conception, let 

 o E represent also the uniform velocity of the rain : very much 

 more rain will now fall on the front of 11 o R, and much less on 

 the bat'k of H o k, than before. In fact, if o m be taken = o E, 



Fig. 11. 



and the angle m o R be made = ROE, and the parallelogram 

 tn E be complete 1, then a raindrop, of which w's real path is 

 M E, would, by the motion of n o K, just graze along the front 

 surface of H o R in the direction M R o, when it arrives at E. 

 Moreover, all the rain which at the beginning of the motion 

 was moving within the angle m o r, which would have fallen on 

 the back of H o R at rest, will now fall on the front of ho r, if 

 in motion. 



" The application of this hypothetical case to that of meteors is 

 obvious, hok now represents the horizon, z the zenith of an 

 observer, and o E the direction and magnitude of the earth's 

 orbital motion. The earth's diurnal motion of rotation is com- 

 paratively too small to be taken into account for our present 

 purposes. So long, then, as OE, the direction of the earth's 

 orbital motion, is in front of the horizon of an observer, there 

 will thereby occur to him an additional flow (and partial com- 

 bustion) of meteors against the earth's atmosphere above him ; 

 and this increased flow will become the greater as the angle 

 ROE becomes greater. If o E be below it R. then the number 

 of visible meteors will thereby be diminished.'' 



Now, if we refer to Fig. 10 we shall see that the observer does 

 not reach the forward part of the earth (with reference to the 

 apex of the earth's way) till midnight, and that the apex rises 

 gradually till it is on his meridian at sunrise. 



■ ' Monthly Xo'.ius, 1864, vol. xxiv. p. 133. 



Here, then, is the reason why the number increases from sun- 

 set to sunrise, based upon the theory of their cosmical origin, 

 and really explainable in no other way. 



> >>w for the yearly conditions as revealed by observation. 



Dr. Julius Schmidt, the Director of the Observatory at Athens, 

 observed, between the north latitudes of 49°'5 and 54°*2, during 

 eight years from 1843 to '850, on an average 470 meteors in 

 every year. These were distributed among the several months 

 as follows, taking an average of the entire series : — 



Month. 



July ... 

 August ... 

 September 

 October... 

 November 

 December 



January ... 



February 



March ... 



April 



May 



June 



Total 



470 



Prof. A. Herschel was the first to point out that this yearly 

 difference, as well as the daily difference in the hourly numbers, 

 arrived at by Coulvier-Gravier, demonstrated the cosmical 

 origin. 



In 1864 he wrote as follows, assuming that the meteorites 

 travelled faster than the earth: — l 



"A season of frequency of aerolites, shooting-stars, and bolides, 

 must be expected to succeed, in all latitudes, three months later 

 than the summer season of the sun ; but, on the other hand, a 

 dearth of meteors, in the spring, one quarter of a year later than 

 mid-winter. In general, and in all latitudes, the meteoric seasons, 

 or seasons of meteoric frequency, must strictly follow the tropical 

 seasons, and three months later in the year. Thus, in the earth's 

 northern hemisphere, the Northern Pole remains directed to the 

 sun from the equinox of March until that of September, and to 

 the course of meteors from the solstice of June to the solstice of 

 December. The greatest frequency of the meteorites will fall 

 about the equinox of autumn, in September and October. This 

 most nearly agrees with the European observations. The meteoric 

 season of Arago may, therefore, be drawn as a consequence from 

 his planetary hypothesis, if it be permitted to change the li nits 

 which he assigns to it by a small quantity — namely, from the 

 Earth's apsides to its solstices in its orbit. 



"The same fact, which appears strongly marked with regard to 

 shooting-stars in the eight years' summary of Dr. Schmidt, is 

 found repeated in a striking manner in the existing ' Northern 

 Catalogues of Star-showers, Fire-balls, and Aeroliths.' The 

 following references may be taken as examples : — 



Number — Number — 



Appearances. July to December. January to Jjne. 



Star-showers from 1800 B.C. 



In M. Quetelet's catalogue 

 ("Physiquedu Globe," 1861) \ 

 Aerolitic meteors, from the 

 Christian era. In Mr. 

 Greg's catalogue (British 

 Assoc. Report, i860) . . 

 Large and small fire-balls. 

 In same catalogue {ibid.) . 



72 



216 



843 



28 



553-' 



It was now pointed out, by Newton 2 and Schiaparelli, 3 that, 

 provided the actual facts of the daily and yearly variation were 

 sufficiently assured, the true velocities of these bodies in space 

 could not be just simply similar to the earth's velocity, nor their 

 paths in space planetary orbits like that of the earth, and of 

 about the same dimensions ; but that as their motion was much 

 faster their orbits would be variously distributed parabolas, and 

 they would consequently be more akin to comets. 



That the movement was really much faster was argued in 



1 Monihiy Xotkcs, vol. xxiv. 



3 Sillittian's Journal, vol. xxxix., 1865; Nat. Acad. Sci., vol. i. ; 

 An 111a ire de V Observaloire de Bruxelles, i856, p. 201. 

 3 Los liondes, vol. xiii. 



