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THE GUIDE TO NATURE 



ning that its path is a curve of this 

 kind. Continued observations on the 

 present comet soon showed, however, 

 that its motion could by no means be 

 accounted for on the assumption of 

 such an infinite path. A complete com- 

 putation soon revealed that its orbit 

 is a very small and narrow ellipse, AC, 

 extending; from bevond the earth's 



later planetary disturbances have since 

 altered this path to the position BC. 



Computation shows that the new 

 comet passed close to Jupiter in 1913. 

 The pull upon it by the Giant Planet 

 at this time must have very greatly 

 altered its path, changing it into the 

 new, small orbit along which it is mov- 

 ing now. Whether before this disturb- 



Figiire 3. Showirg how a comet may be "captured." 



orbit to a very slight distance beyond 

 the orbit of Jupiter. The comet passes 

 completely around this path every six 

 years ; it was nearest the sun on last 

 January 30; and is now rapidly draw- 

 ing away from the earth. 



How the New Comet Was Captured. 



A comet is a great nebulous cloud, 

 composed of meteoric matter, gases, 

 and cosmic dust, which falls toward 

 our sun from the depths of space. It 

 is therefore a visitor, and it can visit 

 us only once unless it is disturbed in 

 its motion. If, however, it happens to 

 pass sufificiently near one of the plan- 

 ets, the gravitational pull of this body 

 may completely alter its path, and may 

 either send it out of our Solar System 

 faster than it entered, or it may cause 

 it to move in a closed orbit and thus 

 prevent its ever leaving us again. 

 Thus, when Tuttle's Comet first fell 

 toward the sun, along the path MPN, 

 Figure 3, it passed so near to Uranus 

 that the disturbing pull of this planet 

 caused it to follow the path AC, and 



ance its path was a parabola, so that 

 it entered our system only three years 

 ago, or whether it is merely one of the 

 older periodic comets whose path has 

 thus been changed, we do not yet 

 know. Further computations will un- 

 doubtedly, however, soon settle this 

 point. 



The continued observation of these 

 periodic comets at their successive re- 

 turns is of the highest interest and 

 value. In at least one case, that of 

 Encke's Comet, the motion was found 

 to be disturbed along part of its orbit, 

 a disturbance which cannot be due to 

 the pull of any known body in our 

 Solar System. 



The April Shooting Stars. 



This is one of the few conspicuous 

 showers of the year, and though not so 

 well known or so numerous in stars 

 as those of August and November, it 

 is still a most interesting phenomenon 

 for the naked eye observer. It should 

 be looked for on the nights from April 

 20 to 22, and if possible at a late hour 



