32 POPULAR LECTURES AND ADDRESSES. 



the surface is 180; and the shortest line on the 

 surface from any one point to any other, must 

 clearly lie along a great circle. Look at your 

 terrestrial globe to illustrate this. The Mercator 

 chart before you, extending from latitude 40 to 

 latitude 80, shows what great circles look like on 

 Mercator's projection. One of the lines is a great 

 circle from Cape Farewell to a point in longitude 

 70 E., latitude 50 N. The other is a great circle 

 from Valentia to Trinity Bay, Newfoundland, along 

 which the original Atlantic cables were laid. 



The oval curves on the Mercator's projection of 

 56, Fig. 14 below, represent what are in reality two 

 circles on the earth's surface, drawn for the purpose 

 of illustrating Sumner's method, to be explained 

 later. They are what are technically called " small 

 circles," their diameters being respectively 100 and 

 80, and their centres inlat. 10 N. 



26. STATION POINTER. The station pointer 

 consists of three rulers turning in one plane round 

 a common centre, with their edges so set as to 

 radiate from this centre, and with a graduated arc 

 showing the inclinations of the edges one to 



