254 THE POPULAR SCIENCE MONTHLY. 



The predictions made in November, 1872, were not so precise as 

 they would probably have been if the comet had been seen in 1866 

 and in 1872, as had been expected. Indeed, astronomers had very little 

 experience as to the meteors of Biela's comet. They were in doubt 

 what showers among those recorded by various observers of meteors 

 as occurring during the last week of November and the first week of 

 December could be associated with this particular meteor system. 

 For until the astronomical significance of meteoric disjjlays had been 

 fully recognized, the observers of shooting stars, even when these were 

 seen in showers, had been more careful to record the brightness and 

 the number of the meteors than their course among the stars. So that 

 the criterion which at present distinguishes one meteor system from 

 another, even though both meteor systems may show falling stars on 

 one and the same night or at one and the same time, is not applicable 

 to most of the records of star-showers. That criterion, it need hardly 

 be said, is the position of what is called the radiant point of the star- 

 shower, the point from which all the meteor-tracks on the sky seem to 

 tend. The reader must not fall into the mistake of suj^posing that 

 every meteor-track absolutely extends from the so-called radiant. On 

 the contrary, it may truly be said that not one such track does or can 

 extend from that point. But each tends from the point in the sense 

 that, if the course pursued by the meteor be supposed to be extended 

 backward in a straight line (or, more correctly speaking, in a great 

 circle of the heavenly sjDhere), the line would pass through the radiant 

 point. The expression is used in the same general sense, and has, in 

 fact, the same significance as the statement usually made about par- 

 allel lines and their vanishing point in perspective. Lines which are 

 really parallel are so drawn in perspective that they all tend from one 

 and the same point, but they do not extend from it. An artist might 

 indeed draw them all in pencil from that point, but he would after- 

 ward rub out pai'ts of the pencil-lines, leaving the rest all tending 

 from the vanishing-point, but none of them extending actually from it. 



Now, what is the radiant point of a meteor system ? It is in real- 

 ity that infinitely remote point from which all the meteors seem to be 

 traveling — the point toward which all the parallel lines on which they 

 are actually traveling seem to converge. No meteor, then, approach- 

 ing the earth on the course thus indicated could possibly seem to move 

 actually from the radiant point. If moving directly toward the ob- 

 server, it would be visible at the radiant point, all the time, not seem- 

 ing to move/rom it ; if not moving directly toward the observer, but 

 on a course parallel to that from the radiant point to the observer, it 

 would be seen, from the beginning to the end of its flight, at points 

 removed from the radiant, but all on a line tending from it. Thus the 



amine the evidence brought forward by others, has committed an offense against scientific 

 morality (scientific morality only, be it understood) such as he can allege against none of 

 those whom he so warmly denounces. 



