THE sun's journey THROUGH SPACE 



away the sun is from us, it would have been absolutely 

 impossible to tell the distance that separates us from any 

 of the millions of other worlds around us. We would forever 

 have remained in ignorance of their mass, which quantity 

 enables us to tell at present the very influence thej^ exert 

 over their neighbors in space. If the sun's distance had 

 not been ascertained, it would have been impossible for us 

 to tell its true size, neither could we have determined its 

 weight or density. Moreover, without being aware of 

 the sun's distance our knowledge also of the distance, 

 magnitude and weight of all the planets would have 

 remained forever unattainable. It is therefore at once 

 apparent how supremely important in all astronomical 

 questions is this unit of measurement of space — the 

 distance between the earth and the sun. There is little 

 wonder then that some of the greatest minds that ever 

 lived, from Aristarchus of Samos, who flourished before 

 the Christian era, down to the present day, have devoted 

 their whole talent and skill in endeavoring to solve, with 

 the least possible error, this grand problem of the sun's 

 distance. 



It is easy to tell the distance between two points on 

 the ground if we can put our chain measure across. The 

 case, however, is very different when we attempt to 

 measure any inaccessible object when a river or other 

 obstacle bars our way. Here we have recourse to the 

 method adopted by the land surveyors who, by means of 

 an instrument for measuring angles and known as the 

 theodolite, can tell the distance an object is away in yards 

 or feet with the same degree of accuracy as if thej^ had 

 been able to carry their chain measure accross the river, 

 for instance. This method depends upon certain well- 

 known properties of the triangle and fully described in 

 works on trigonometry from which it follows, if we know 

 the length of one side and two angles of any triangle, we 

 can then always calculate with certainty the other angle 



