272 HISTORY OF SCIENCE: 



system by the circumstance that it applies equally to all the stars, and 

 to the nebulae and star-clusters. The identity, too, of the materials 

 of the stars with some of the chemical elements of which the earth is 

 composed one of the most striking discoveries of modem science, 

 which will be discussed in a subsequent chapter harmonizes with the 

 nebular hypothesis in a remarkable manner, as do many modern ob- 

 servations in celestial physics. It was the work of Newton to show 

 that the great law of gravitation governed all the motions of the planets 

 of our system ; but, as he was unable to find in the laws of gravitation 

 and of motion the necessary stability of that system, he conceived that 

 the Deity must occasionally interfere to regulate His work. Laplace 

 showed that the laws of gravitation and of motion assure the eternal 

 stability of the solar system, and he demonstrated that the threatening 

 perturbations which affect the planetary orbits are, in reality, but slight 

 oscillations about a mean position " immense pendulums of eternity 

 which beat centuries as ours beat seconds/' And as he found the law 

 of gravitation to be efficient in the preservation of the system, so he 

 conceived it might also have operated in its formation. 



The great project of Laplace was accomplished by the publication 

 of his "Mecanique Celeste" a splendid monument of intellectual power, 

 the publication of which forms an epoch of the history of the human 

 mind. This modern Almagest uniformly applies to astronomy and 

 general mechanics th.e highest power of mathematical analysis. The 

 first and second volumes were published in 1799, and treat of the laws 

 of equilibrium and motion, gravitation, the centre of gravity, the figures 

 of the celestial bodies, the tides of the ocean and of the atmosphere, 

 the movements of the celestial bodies round their centres of gravity, 

 the precession of the equinoxes, the moon's libration, the theory of 

 Saturn's ring. The third volume, published in 1 802, treats of the theory 

 of the motions of the planets and of the moon. In the fourth volume, 

 which appeared in 1805, the author investigates the theory of the satel- 

 lites of Jupiter, Saturn, and Uranus; the theory of comets ; atmo- 

 spheric refraction ; the barometer ; the masses of the planets, etc. The 

 fifth volume, published in 1825, treats of the figure and rotation of the 

 earth, attraction and repulsion, elastic fluids, capillary phenomena, the 

 history of the various researches relative to the system of the world, 

 etc. Laplace published in 1796 a work bearing the title of "Exposi- 

 tion du Systeme du Monde" from which persons unacquainted with 

 mathematics may obtain a just knowledge of the methods to which 

 modern physical astronomy owes its astonishing progress. The pro- 

 duction is distinguished by great clearness and simplicity of style, com- 

 bined with elegance and a scrupulous precision. Another publication 

 of Laplace was on " Probabilities," and it was worthy of the author of 

 the " Mecanique Celeste" This illustrious mathematician died in 1827. 

 Like Newton, he possessed the humility of a true philosopher, and his 

 last words were, " It is little that we know, but what we are ignorant 

 of is immense." 



