ERA OP NEWTON, HALLEY, AND HERSCHEL 47 



four planets Ceres, Pallas, Juno, and Vesta, revolving round the sun at a mean distance 

 of one hundred millions of miles from Mars, so small as only to be telescopic objects. 

 This discovery we owe to Piazzi, Olbers, and Harding. Some singular features, without 

 parallel in the planetary system, such as then: close contiguity, the intersection of their 

 orbits, with their diminutive size, Vesta not being much larger than the Spanish 

 peninsula, led to the surmise that these bodies are fragments of a planet which once 

 revolved in their mean path with a magnitude proportionate to that of its neighbours. The 

 possibility of such a disruption cannot be denied the revolution of the fragments round 

 the sun would follow in obedience to the mechanical laws by which the system is governed 

 but the point is obviously one of those questions which must remain entirely hypothetical. 



The career of planetary discovery which began with the century, was resumed in the 

 year 1845 ; and has since been continued with most surprising results. Another miniature 

 orb, Astreea, discovered by M. Hencke, was then added to the family of minute worlds 

 rolling between Mars and Jupiter; and in one year alone, 1852, no less than eight such 

 bodies were found. The known number at the time of writing these lines (1st of September 

 1857) is forty-five. Besides this, in the present age, the members of the solar universe 

 have been increased by the detection of the primary planet Neptune, attended with a 

 satellite ; and of an eighth satellite of Saturn, called Hyperion, remarkable for its 

 simultaneous discovery by independent observers, in 1848, Mr Lassel of Liverpool, and 

 Mr Bond of Cambridge, in the United States. The addition of a primary planet to our 

 system demands a brief notice. 



Observations upon Uranus had shown the motions of that planet to present great 

 irregularities, which could not be explained by the action of Jupiter and Saturn ; and 

 after carefully examining the analytical theory of Uranus, Leverrier, a young academician 

 of France, in the summer of 1846, published the elements of an undiscovered planet, 

 the cause of the perturbations. He boldly predicted its existence, calculated its mass, and 

 referred to its place in the heavens ; and scarcely a month afterwards, on the 23rd of 

 September, the hitherto concealed object was found by M. Gallc of Berlin. But it has 

 only been by accidental circumstances that France has the honour of this remarkable 

 achievement. Upon retiring from the chair of the British Association, a fortnight before 

 the observation of M. Galle, Sir John Herschel, in remarkable words, referred to the 

 astronomical events of the past year, observing that it had given a new planet (Astrea) 

 to our list, and adding, " it has done more, it has given us the probable prospect of the 

 discovery of another. We see it as Columbus saw America from the shores of Spain. 

 Its movements have been felt trembling along the far-reaching line of our analysis, with 

 a certainty hardly inferior to that of ocular demonstration." This striking paragraph, 

 as subsequently explained, had a twofold reference to the calculations of Leverrier, and 

 to a similar investigation previously completed by Mr. Adams of Cambridge, the in 

 dependence of the investigations, and their very nearly coincident results, justifying the 

 confidence so strongly expressed by the speaker. Mr. Adams commenced his theoretical 

 researches in January, 1843, recommenced them upon larger data in February, 1844, and 

 obtained results for the heliocentric longitude, eccentricity of orbit, longitude of perihelion 

 and mass of an assumed exterior planet, deduced entirely from unaccounted-for perturba 

 tions of Uranus. These results were communicated to Mr. Challis, the Professor of 

 Astronomy at Cambridge, in September, 1845. In October they were in the hands of 

 Mr. Airy, the Astronomer Royal, whereas Leverrier's labours were not made public till 

 the June of the year following. They were not then so complete as those of Mr. Adams, 

 indicating merely the probable position of the hypothetical planet, while the latter had 

 given values respecting its mass and the form of its orbit. The correspondence between 

 two independent inquiries as to position inspired confidence, and Mr. Airy recommended 



