446 THE POPULAR SCIENCE MONTHLY. 



of these bodies pass daily into the earth's atmosphere, of which about 

 seven millions and a half are large enough to be seen with the naked 

 eye on a clear night, and in the absence of the moon. 



From the direction and swiftness of their flight, it is manifest that 

 meteors are visitors from without. They plunge into our atmosphere, 

 and the resistance to which they become then suddenly exposed must 

 raise them to a temperature which exeeds that of the most intense 

 furnace. The heat is enough first to melt and then to dissipate in 

 vapor the most refractory substances, and it only now and then hap- 

 pens that even a part of a meteor escapes this fate, and reaches the 

 ground. They are for the most part lost in vapor ere they get within 

 several miles of us. The difficulty, indeed, is not to account for their 

 incandescence, but to see why they do not emit a greater flood of 

 light where the heat must be so intense. And, in fact, they can not 

 be other than very small bodies, or they would be much brighter. 

 The average weight of those visible to the unassisted eye appears to be 

 under an ounce, and the telescopic ones, of course, are much lighter. 



Meteors may be distributed into two very obvious classes casual 

 meteors, which dart irregularly through the sky, and meteoric showers, 

 which stream into our atmosphere in one definite direction, and at 

 stated intervals of time. We are concerned at present with the me- 

 teoric showers. Many such are known to exist, of which the principal 

 are the August shower, through which the earth passes every year 

 upon the 9th, 10th, and 11th of August, and the great November 

 shower, which is discharged upon the earth three times in a century. 

 The November meteors are those about which most is known, and it 

 was of these, therefore, that the lecture chiefly treated. 



To make their history intelligible, it is necessary to explore, in 

 some degree, the regions from which they come. For this purpose 

 your attention is called to this great diagram, every hundredth of an 

 inch upon which represents a distance in nature equal to the interval 

 between the earth and the moon.* The distance from the earth to 

 the sun on this diagram is a decimetre, that is, four inches'; and, on 

 the same scale, the nearest fixed star would have to be placed at a 

 distance of twenty kilometres, or upward of twelve miles. 



In these vast celestial spaces, there are no rails over the rough- 

 nesses of which the train must be made to rattle, if it is to move at all ; 

 there are no wheels to be worn out ; there is no air in which a wind 

 must be produced, or through which noise will be propagated. The 

 music of the spheres is not a sound audible to the ear, and an impedi- 

 ment to motion : it is harmless, it is altogether good, it is the pleasure 

 of the human mind when it understands the great works of nature. 

 There is no thundering along through the heavens. All is silence and 

 peace round the planets as they swiftly glide. Bodies which sweep 



* The scale of the diagram exhibited was rather more than forty times the scale of 

 the accompanying woodcut. 



