THE sun's journey THROUGH SPACE 



to US, and from these results the solar parallax has 

 beeti indirectly worked out. This is known as the 

 trio-onometrical method. It should be remembered that if 

 only the distance between any two planets is found, the 

 distance of all the others follows as a natural consequence 

 of the discovery of Kepler's great law, that : ** The squares 

 of the periodic times are proportional to the cubes of the 

 mean distances." The task, therefore, is only to find out 

 the scale upon which the solar jrystem has been formed, as 

 the relative position of every member is already very 

 accurately known. 



As early as the year 1670 the French Academy of 

 Science sent out an expedition to Cayenne to take trigon- 

 ometrical measures of Mars in order to compare with those 

 made in France, but the results were not very conclusive 

 owing to the inferior instruments then in use. Little 

 better results were obtained in 1752 at the Cape of Good 

 Hope by Lacaille, who fixed the sun's parallax at 10", 

 from which the sun's distance would be 82,000,000 miles, 

 an amount we know to be very far out. 



As Mars is particularly well placed, every fifteen 

 years, to make such observations on account of its close 

 proximity to the earth, full advantage has been taken of 

 such periods. Owing to the favorable conditions of the 

 year 1857 i'^ particular. Dr. Gill succeeded in obtaining 

 excellent measurements of Mars in iVscension Island, and 

 deduced 8.780" as the sun's parallax, corresponding to a 

 distance of nearly 93,000,00c miles. Of recent years some 

 of the minor planets, which revolve between Mars and 

 Jupiter, have been utilized to arrive at the true distance of 

 the sun, and many astronomers are of opinion the most 

 satisfactory results of all are to be obtained by a careful 

 examination of these tiny worlds, invisible though they 

 are to the naked eye. 



The rare astronomical event, known as the transit of 

 Venus, is associated with some of the most noted attempts 



