THE sun's journey THROUGH SPACE 



which the semi-diameter or radius of the earth would sub- 

 tend as viewed from the centre of the sun. Once this ex- 

 act amount is found we have all the data required to 

 calculate with precision the distance between the earth 

 and the sun. 



Although elaborate arrangements were made to observe 

 the transit of 1761 in different places, unfortunatel}^ 

 cloudy weather and othei' circumstances practically 

 defeated the first attempt. The transit of 1769 created 

 more enthusiasm and with it came a greater determination 

 to succeed. Special expeditions were accordingly sent out 

 by the governments of various European countries to wit- 

 ness the event. It was in this year that the famous Cap- 

 tain James Cook, the first man to sail around the world, 

 was sent to Otaheite in the Pacific Islands to observe the 

 transit of Venus, and a party of astronomers from Green- 

 wich were located at Fort Prince of Wales, Hudson Bay, 

 while many observers were stationed in remote parts of 

 the globe. After an exhaustive examination of all the 

 available results of these two great events, Prof. Encke, of 

 comet fame, determined the solar parallax to be 8.5776", 

 which gave 95,300,000 as the sun's distance. This 

 amount was accepted for many years and became embodied 

 in all works on astronomy, but doubts as to its absolute 

 accuracy were raised in 1854 by the evidence of a new 

 method based upon gravitational principles, which we will 

 refer to later on. 



No one will wonder at these discrepancies who realizes 

 the infinitesimally small quantities astronomers have to deal 

 with in computations of this kind. A hair-breadth of 

 difference in observation will throw out the result by many 

 thousand miles in actual measurements, and this fact only 

 emphasizes the conclusion that, however perfect this theory 

 may be, yet in prac«tice it taxes human ingenuity and refine- 

 ment to its fullest capacity. Lest any of you should be 

 tempted to say, after listening to my remarks, like Mr. 



