OLAUS ROEMER 67 



300,000 kilometres a second; he laid his calculations in 1676 

 before the Academy in Paris. He at first met with much 

 opposition, which, however, was for the most part only based 

 upon Descartes' opinion that the propagation of light is 

 instantaneous. But Huygens and Newton immediately 

 supported Roemer; they saw in it Galileo's idea, that the 

 velocity of light could be measured by its retardation over 

 great distances, brought to realisation. The correctness of 

 Roemer's conclusion was only put beyond doubt, after his 

 death, by Bradley's discovery of aberration; and a hundred 

 and seventy years later, the velocity of light was measured 

 for the first time over terrestrial distances by Fizeau. 



Roemer left France with many other fine spirits as a per- 

 secuted Lutheran in the year 1681, and returned to Den- 

 mark, where he then became Director of the Observatory, 

 and finally Burgomaster of Copenhagen. He was chiefly 

 responsible for the general introduction of the telescope as 

 a means of astronomical measurement; thus the meridian 

 circle found in every observatory was his invention. His 

 very extensive observations in Copenhagen, made with ap- 

 pliances of this kind, were lost, not long after his death, in 

 the great fire which devastated the town. 



CHRISTIAN HUYGENS 

 1629-1695 



Huygens was Galileo's great and equally gifted successor 

 in almost every respect; and after Kepler, the most active in 

 preparing the way for Newton's investigations, which then 

 for a long time represented the completion of the first in- 

 sight obtained by humanity into a part of the great process 

 of nature. He was, like Galileo, through and through an 



