174 LIGHT SCIENCE FOR LEISURE HOURS. 



that there were one meteor stream lying in or near 

 the plane of the earth's orbit and close to the sun, while 

 a little farther away from him there were another, 

 crossing the plane of the earth's orbit at a considerable 

 angle, then, as the earth in her motion came behind 

 the former, she would be several days in its shadow. 

 Suppose now that in the course of this time she came 

 behind the second or thwart system also. Then for a 

 day or two, or perhaps three, she would be in the 

 shadow of both these meteor systems. I am not by 

 any means speaking wildly, but most moderately, in 

 saying that small and widely scattered though the 

 individual meteors might be, the effect of their inter- 

 position could hardly fail to be recognisable. Nay, 

 oddly enough, the smaller the meteors were individually 

 (with a distribution of so much meteoric matter per 

 cubic mile) the greater would be the effect of their 

 interposition. 



But, it may be said, if there are meteoric streams 

 such as these, capable of casting an effective shadow 

 on the earth, these streams ought to be visible during 

 total eclipse. Of course, individual meteors could not 

 possibly be seen. A meteoric mass ten miles in 

 diameter, close to the sun's surface, would be utterly 

 invisible in the most powerful telescope ever yet made 

 by man. What, then, would be the chance of seeing 

 bodies whose diameters (even those of the largest of 

 them) would be measurable by inches? But if a 

 meteoric stream can cut off a measurable or recognis- 

 able quantity of solar heat, it must of necessity 



