LE VERRIER AND ADAMS' PLANET. 



scale upon which the orbital motion of this planet takes place, we 

 have represented in tig. 5, the orhit of the earth, E, E', E", E"', 

 the distance of E from s, the sun, being 100 millions of miles ; 

 s N will then be upon the same scale, the distance of Neptune from 

 the sun. 



Although it is easy by this expedient to convey a sufficiently 

 exact notion of the relative distances of these planets from the 

 sun, it is by no means so easy to acquire any adequate idea of 

 their actual distances, or what is the same, of the scale of the 

 solar system. 



To obtain, even in the case of magnitudes infinitely less than 

 these, any just notions, it is necessary to compare them, and, as 

 it were, to measure them by some standard of magnitude, with 

 which we have a practical familiarity. Let us see then, whether 

 by such an expedient we can obtain some notion, however faint, 

 of the scale of the solar system, at the extreme limit of which 

 Neptune moves. 



19. Every one is at this time familiar enough, with the motion 

 of a railway train having a given speed, say, for example, 30 

 miles an hour ; we know that in such a train, moving with that 

 speed, stoppages included, we can go from London to Liverpool 

 in 7 hours ; in what time, let us ask, could we be transported in 

 such a train from the sun to the earth ? The distance, as already 

 stated, is 100 millions of miles ; if this be divided by 30 we shall 

 find the number of hours which such a journey would take, this 

 number would therefore be 3,333333 hours. If this be divided 

 successively by 24 and by 365| we shall find the number of days 

 and of years in such a journey ; the result of such a calculation 

 in round numbers will show that such a train will take 380 years 

 to move from the sun to the earth. 



But Neptune being, as we have seen, 30 times more distant 

 than the earth from the sun, it would take the same train an 

 interval 30 times longer to move to that planet; we therefore 

 arrive at the astounding conclusion that a railway -train moving 

 constantly without stoppage would take 114000 years to move from 

 the sun to Neptune, that is to the extreme limit of the solar system. 



The circumference of a circle, whose diameter is 6000, is 18849 ; 

 now since the diameter of Neptune's orbit is 6000 millions of 

 miles, its circumference is 18849 millions of miles, and round this 

 circumference the planet moves in 164'6 years, and it therefore 

 moves at the rate of 114,500000 miles per year, or 313500 miles 

 per day, or 13000 miles an hour. 



Such is the colossal scale on which the movements of the system 

 are conducted. 



20. It will doubtless be asked, whether the magnitude of this 

 186 



