28 POPULAR LECTURES AND ADDRESSES. 



of the difficulty in understanding the methods of 

 spherical astronomy taught there for subsequent 

 daily use at sea, would be smoothed down by aid of 

 either the celestial or the terrestrial globe or both. 

 The mystery of great circle sailing is done away 

 with by merely looking at a terrestrial globe ; and 

 in actual practice at sea, a terrestrial globe would 

 be exceedingly useful in laying out great circle 

 courses, and planning the courses to be actually 

 sailed over, and for approximate measurements of 

 great distances on the earth's surface, instead of 

 laboriously (and sometimes with useless exactness) 

 working out these questions by a blind use of 

 logarithms. The celestial globe would be exceed- 

 ingly useful at sea for facilitating the identification 

 of stars to be used for finding the ship's position by 

 altitudes, or correcting the compass by azimuths. 

 A blackened globe, upon which circles can be 

 drawn in chalk, is also useful at sea for approxi- 

 mate solutions of some problems which occasionally 

 occur, and is indispensable in a navigation school 

 whether on shore or on board ship, for the in- 

 struction of young officers. Still the main work 



