124 



S. L. Penfield — Stereogram hie Projection. 



tively 65° 45' and 34° 45' West of the meridian of Queens- 

 town. By taking the radii from scale No. 1, figure 3, the two 

 meridians are quickly drawn. New York, being in latitude 

 40° 4CK N., is 49° 20' south of the pole. Its position is deter- 

 mined by locating the point 40° 40' N. on the central meridian, 

 and constructing the small circle with radius 49° 20' taken 

 from scale No. 2, figure 3. In a similar manner, Rio de Janeiro 

 is located. The figure also indicates another method of locat- 



€-15' w 



ing Rio de Janeiro. On the equator locate the points^? and ^/ 

 at 23° from the crossing of the meridian of Rio de Janeiro. 

 The intersection of the meridian being 34° 45' (43° — 8° 15') 

 from the divided circle, the points p and p' are respectively 

 11° 45' and 57° 45 / from the divided circle. Now by finding 

 the center and constructing the small circle, Rio de Janeiro is 

 located. To measure the distances, match the zero point of 

 protractor No. II with Queenstown, swing the protractor so 

 that its center corresponds with that of the plate, and note the 

 position of the points plotted. Thus plotted, the distances from 

 Queenstown to New York and Rio de Janeiro were found to 

 be respectively 45° 15' and 80° 52', calculated 45° ll 7 and 80° 

 47'. Plotted in this way it is seldom that the error exceeds 

 6'; the average error is less than 4'. It is a decided advantage 

 to be able to determine any distance by one reading of the 

 protractor, rather than by two readings and a subtraction, as 

 illustrated by figure 22. 



It may be seen from the foregoing demonstrations that if 

 there were maps of the northern and southern, and eastern and 



