SCIENTIFIC LITERATURE. 



553 



outline, the reader will gather, first, 

 that the book possesses a certain origi- 

 nality of its own, it stands for solid 

 work by its author and affords one the 

 pleasure that such work gives. Second, 

 it is attractive, because it marks a stage 

 of transition. Ten years hence, these 

 clean-cut distinctions within experience 

 will have become impossible. The work 

 is, therefore, to be commended as a 

 faithful and forthright representation 

 of that type of thinking which, though 

 well aware of the futilities of eighteenth 

 century dualism, has not yet awakened 

 to the demands of twentieth century 

 system. Being thus a type, it is well 

 worth taking into consideration. 



STATIONARY RADIANTS TO SHOW- 

 ERS OF SHOOTING STARS. 

 The radiant of a shower of shooting 

 stars is the point or area from which 

 all the stars appear to move when per- 

 spectively projected on the celestial 

 vault. If the tracks of a shower of 

 meteors are laid down on a star map, 

 and if these tracks are prolonged, all of 

 them will intersect in a point, or, at 

 least, within a small area — the radiant. 

 The meteors are really moving in paral- 

 lel straight lines in space. Their paths 

 are perspectively projected into great 

 circles of the celestial sphere, and have 

 a common vanishing point. The case is 

 easily understood by that of the 'sun 

 drawing water,' which is often seen 

 about sunset. The rays of the sun are 

 really parallel, but they seem to radiate 

 in all directions from the sun's disc in 

 great circles that have a common van- 

 ishing point. 



This perspective theory demands 

 that the radiant point of a shower of 

 meteors should rise, culminate and set 

 by the earth's diurnal motion, pre- 

 cisely as the sun, or a star, rises, 

 culminates and sets. The meteors on 

 any night do, in fact, radiate from 

 spots Avhich remain fixed among 

 the stars, and which rise, culmi- 

 nate and set as do the stars them- 

 selves. If the shower continues for 

 many nights (like the Perseid shower, 



for instance) the place of the radiant 

 usually shifts among the stars, as it 

 ought to do, since its position is due 

 to a geometric configuration which 

 changes as the earth moves. The per- 

 spective appearances change as the place 

 of the spectator is altered by the earth's 

 motion in its orbit. Mr. W. F. Den- 

 ning, of Bristol, England, an experi- 

 enced and assiduous observer of meteors, 

 reports that he has found cases where 

 the appearances differ from these nor- 

 mal conditions. For certain showers 

 of meteors, the radiant does not change 

 its place among the stars as the 

 earth moves in its orbit, but, on the 

 contrary, the radiant remains sta- 

 tionary for weeks. A typical case of the 

 sort is the shower of the Orionids. This 

 shower persists for about two weeks 

 (October 10-24), and the radiant remains 

 stationary near the star v Orionis, in- 

 stead of shifting with the earth's mo- 

 tion as the laws of celestial perspective 

 demand. 



No satisfactory explanation of such 

 stationary radiants has been forthcom- 

 ing; and many astronomers have doubt- 

 ed the correctness of Mr. Denning's ob- 

 servations on that account. Granting 

 that the observations are correct, an ex- 

 planation of the phenomenon has been 

 given by Professor von Niessl, of Briinn, 

 and this explanation was briefly report- 

 ed by Prof. Alexander Herschel at a 

 recent meeting of the Astronomical So- 

 ciety of France. From a rather meager 

 account of the report it appears that 

 M. von Niessl has sought for a path 

 of a meteor stream so situated in space 

 and so curved that the observed phe- 

 nomena would necessarily follow. Given 

 the phenomena and the fact that they 

 are produced by the perspective projec- 

 tion of the actual paths of meteors in 

 space, he has inquired what the paths 

 must be to satisfy all the conditions. 

 If we assume swarms of meteors, mov- 

 ing with small velocities in space, in 

 hyperbolic orbits nearly parallel, the 

 orbits being asymptotic to the sun, me- 

 teors proceeding from such swarms 

 would seem to have a stationary radi- 



