The November Shooting Stars. 19S 



combination of their own actual motion, and the earth's motion 

 applied in a reversed direction) . 



These suppositions being made, we can have no difficulty 

 in selecting a suitable point of space from which in imagination 

 to view our earth. The " radiant point " is clearly the proper 

 point to select. If the reader, therefore, will suppose himself 

 somewhere in space, between e and /jl Leonis, aud armed with 

 sufficient optical power, he will be prepared for the examination 

 of the illustrative Figs. 1 and 2. In these the earth is supposed to- 

 be viewed from such a direction; in Fig. 1, at about a quarter 

 past twelve, and in Fig. 2, at about a quarter past two, Green- 

 wich solar time, on November 14th, in any year. The shaded 

 half of each hemisphere is the portion turned from the sun, the 

 apparent boundary of this portion being a straight line, because 

 the radiant point (as respects its longitude) is situated very nearly 

 in the direction towards which the earth is moving at the time. 

 But since the radiant (as respects latitude) was raised some 10° 

 to the north of the ecliptic, the north pole of the earth is brought 

 more into view than it would be to an observer placed at a 

 point towards which the earth is actually moving at the time. 

 In fact, the presentation of the earth towards the radiant point 

 happens to be almost exactly the same (as to inclination of the 

 polar axis) as the presentation of the earth towards the sun at 

 the time of summer solstice. Without entering farther into 

 these points, it will suffice to say that Figs. 1 and 2 are the 

 results of mathematical calculation and careful construction — 

 not imaginary figures set down partly at random, as is too 

 often the case with illustrations of this sort. I am particular 

 to mention this, because when it is known that an astronomical 

 picture represents actual facts, as closely as possible, the 

 student will undertake the study of the picture with some hope 

 of information and instruction, whereas the study of illustra- 

 tions (so-called) not carefully constructed — and nine out of ten 

 figures in our works on popular astronomy fall under this 

 category — is often worse than unprofitable. 



Around London and Calcutta in Map 1, and around 

 London and Cape Town in Map 2, oval and circular spaces are 

 indicated. It is necessary to explain the meaning of these. 

 Assuming the depth of our atmosphere to be about seventy 

 miles — or, at any rate, that meteors are not commonly visible 

 at greater heights — it is easily shown that the segment of 

 atmosphere cut off by a plane touching the earth at any pointy 

 has a circular base about 1,500 miles in diameter. Thus 

 neglecting the effects of refraction which would slightly 

 increase the dimensions of the segment, we have this result, 

 that no meteor can be seen from any point of the earth's sur- 

 face further than 750 miles from the point over which such 



VOL. XII. NO. III. 



