THE NEW PLANETS. 



2. Almost every one who knows anything beyond the limits of 

 the most ordinary education*, is aware that the solar system, as it 

 was known until the last hundred years, consisted of six planets, 

 which, proceeding outwards from the sun, received the mytholo- 

 gical names of Mercury, Venus, the Earth orTellus, Mars, Jupiter, 

 and Saturn. It is now about three-quarters of a century since the 

 late Sir William Herschel added one to this number, by the dis- 

 covery of the planet since called Uranus, revolving outside the 

 orbit of Saturn. 



3. On comparing the successive distances of these several 

 planets from the sun, it was observed by Kepler, that a remark- 

 able numerical harmony prevailed among them. Thus, if we 

 begin from the nearest planet to the sun, Mercury, and measure 

 the intervals between planet and planet proceeding outwards, it 

 will be found that each successive interval is almost exactly 

 double the one before, subject, nevertheless, to a striking excep- 

 tion in the case of the interval between Mars and Jupiter. 



4. Although this remarkable arithmetical harmony was not 

 fulfilled with that numerical precision which characterises some 

 other astronomical laws, there was, nevertheless, so striking an 

 approximation to it as to produce a strong impression, that it 

 must be founded upon some physical cause, and not merely acci- 

 dental. The near approximation to its exact fulfilment, supplied 

 grounds for a very reasonable conjecture, that a planet was 

 wanting in the system, whose position between Mars and Jupiter 

 would be such as to fill the vacant place in the progression of 

 distances. 



To show how strong the analogy was in favour of such a sup- 

 position, we have placed in the following table the succession of 

 calculated distances from Mercury's orbit, which will exactly 

 fulfil it, in juxtaposition with the actual distances of the planets, 

 the earth's distance from the sun being the unit. 



By comparing these numbers, it will be apparent, that although 

 the succession of distances does not correspond precisely with a t 

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