A Century of Science 5 



It is not only in chemistry, however, that the 

 marvellous advance of science has been exhibited. 

 In all directions the quantity of achievement has 

 been so marked that it is worth our while to take 

 a brief general survey of the whole, to see if haply 

 we may seize upon the fundamental charaQteristics 

 of this great progress. In the first place, a glance 

 at astronomy will show us how much our know- 

 ledge of the world has enlarged in space since the 

 day when Priestley set free his dephlogisticated 

 air. 



The known solar system then consisted of sun, 

 moon, earth, and the five planets visible to the 

 naked eye. Since the days of the Chaldsean shep- 

 herds there had been no additions except the 

 moons of Jupiter and Saturn. Herschel's telescope 

 was to win its first triumph in the detection of 

 Uranus in 1781. The Newtonian theory, promul- 

 gated in 1687, had come to be generally accepted, 

 but there were difficulties remaining, connected 

 with the planetary perturbations and the inequali- 

 ties in the moon's motion, which the glorious la- 

 bours of Lagrange and Laplace were presently to 

 explain and remove, labours which bore their full 

 fruition two generations later, in 1845, when the 

 discovery of the planet Neptune, by purely mathe- 

 matical reasoning from the observed effects of its 



