ARTICLES 



THE BRITISH ECLIPSE EXPEDITION 

 TO CHRISTMAS ISLAND 



By H. spencer JONES, M.A., B.Sc. 

 Chief Assistant, Royal Observatory , Greenwich 



The inception of the popular attention which has within the 

 last few years been focused on Einstein's Generalised Theory 

 of Relativity may be traced back to the report to the Royal 

 Society of the results obtained by the two expeditions sent 

 out under the auspices of the Joint Permanent Eclipse Com- 

 mittee of the Royal and the Royal Astronomical Societies to 

 observe the eclipse of 19 19, May 29. It was at that eclipse 

 that the first really serious attempt was made to test whether 

 rays of light were bent by the gravitational field of the sun, 

 and if so, by what amount. The expedition to Brazil was 

 favoured with excellent conditions during the eclipse, whilst 

 that to Principe, though considerably interfered with by cloud, 

 was fortunately able to secure some observations which, in- 

 complete as they were, tended to support those obtained in 

 Brazil and to join with it in confirming the conclusion deduced 

 by Einstein from his theory. The results were announced at 

 a meeting of the Royal Society in November 1919 and attracted 

 widespread attention. Many who had hitherto been very 

 sceptical with regard to the theory began, as a result of this 

 further success which it had gained (its success in accounting 

 for the perihelion motion of the planet Mercury being already 

 well known), to look upon it with more favour. Others took 

 up the attitude that further confirmation was desirable before 

 such a radical revolution as the theory demanded in scientific 

 thought could be accepted. 



It was unfortunate that the results obtained at the eclipse 

 of 191 9 were not such as to gain general acceptance. Two 

 instruments were used in Brazil and their results were discor- 

 dant. As has been very general on eclipse expeditions, hori- 

 zontal telescopes had been employed, the fight from the sun 



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