MODERN SCIENCE. 201 



perturbations of the celestial bodies, and even the existence of 

 as yet undiscovered bodies. It is a striking example of the 

 force of prejudice and early training that the great Leibnitz 

 opposed Newton's conclusions. Of all the discoveries made 

 by mankind, Newton's is the sublimest not only the greatest, 

 but the most universal. Hipparchus's discovery of the pre- 

 cession, so marvellous considering the conditions of science in 

 his time, and Laplace's Nebular Hypothesis, so magnificent 

 as a conception, and so imposing as a scientific solution of 

 the problem of universal genesis, must be placed below the 

 discovery of Newton. It may be added that his work 

 "PRINCIPIA" constitutes par excellence the true MODERN 

 ORGANUM of the scientific method : the laws which he dis- 

 covered are wonderful, but his example of the manner of 

 establishing them is nearly as marvellous. " The scientific 

 procedure which he disclosed has been to a great extent 

 the germ of a vast development in the physical and 

 mathematical sciences." The philosophical significance of 

 this discovery was at least equal in importance to its 

 physical meaning for the truth was demonstrated that the 

 government of the planetary system "is under necessity/' 

 and that "it is impossible for the laws presiding over it 

 to be other than they are." 



16441710. Roemer discovered the VELOCITY OF LIGHT 

 (1676) one of the greatest discoveries in astronomical 

 and physical science. By a careful observation of the 

 eclipses of Jupiter's moons, he found that instead of recurring 

 at fixed times and intervals, they regularly varied 16 

 min. 36 sec. every six months. If one for instance, say 

 the first satellite, which passes into Jupiter's shadow at equal 

 intervals (of 42 hours 28 min. 36 sec.), suffers occultation 

 (hiding) on the 1st of January, at eight o'clock at night, it is 

 found to suffer occultation on the 1st of July at 8 hours 16 min 

 36 sec. of the clock a retardation of 16 min. 36 sec. Roemer, 

 having ascertained this phenomenon, rightly inferred the cause 

 to be due to our being in January nearer to, and in July further 

 from, Jupiter by the whole width (or diameter) of the earth's 

 orbit viz. 190 millions of miles, and the light of Jupiter there- 

 fore taking 16 min. 36 sec. longer to reach us in July than in 



