i\EW MEASUREMENTS OF THE DISTANCE OF THE SUN.« 



By A. R. HiNKS. 'SI. A. 



Wlion T roroivpd the honor of an invitation to locturo at tho School 

 of Military Engineering' on some astronomical subject, I had little 

 difficulty in making my choice of a topic. There is just one subject 

 on Avhich I may speak with some little first-hand knowledge; and 

 b}' great good fortune that subject is concerned with a problem which 

 has both in its nature and its history a connection with the Corps of 

 Ro^^al Engineers. 



The problem of the determination of the distance of the sun is, in 

 some respects at least, the most fundamental in the whole range of 

 astronomy, for the number which rejDresents it is involved in almost 

 any calculation of distances and masses, of sizes and densities, either 

 of planets or their satellites or of the stars. The distance of the sun 

 bears somewdiat the same relation to other problems of celestial sur- 

 veying as the size and shape of the earth bear to terrestrial. It may 

 not always appear on the surface, but it is generallv concealed some- 

 where in the depths of the calculations. And I am compelled to 

 confess that in one respect the earth measurers have the advantage 

 over astronomers. The utmost that the astronomer can do is to 

 show that the divStance of the sun is so many times the radius of the 

 ( arth. But ask him to put it into miles and he is powerless to do 

 so until the geodesists have told him how large the earth is; and it 

 is there that, in the very nature of the case, we are compelled to 

 depend in the end upon the scientific labors of your corps. 



« Lecture delivered at the Royal Engineers" Institute on February 0. inO.^. 

 Reprinted, by permission, from the Royal Engineers" .Journal. \'olume II. No. 1. 

 July, 1905. Chatham, England. Royal Engineers' Institute. 



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