Geographical Maps and Sailing Charts. 



253 



Projection upon the plane of the Equator. — This is the 

 simplest kind of stereo-graphic projection. The meridians 

 appear as straight lines, figure 4, and the parallels as concentric 

 circles. The lengths of the radii for describing the parallels 

 may be determined by projection,* but are best taken from 

 tables, as described in a note at the close of this article. 

 Attention may be called to the fact that, in spite of distor- 

 tion, the shapes of the countries shown on the map are admir- 

 ably preserved, as may be seen by comparing the map with a 

 globe. 



In order that such a subject as Mathematical Geography may 

 be in every way practical it must be made exceedingly simple. 

 In the writer's earlier communication, already referred to, 

 Plate II represented an engine divided projection upon the 

 plane of the equator ; that is, a system of meridians and par- 

 allels projected with practically absolute accuracy. In connec- 

 tion with such a plate it is now proposed to use an engine 



divided scale, figure 5, printed on tracing paper, which may 

 be placed over a projection of corresponding size, between any 

 two meridians. To locate a place of given latitude or longi- 

 tude, for example New York, 40° 43' K, 74° W., it is only 

 necessary to adjust the scale between the appropriate merid- 

 ians on the map, find the desired location, and then puncture 

 with a needle point through the scale to the plate below. 

 With an engraved plate one foot in diameter and an accom- 

 panying scale, figure 5, it would be crude plotting if places 

 were not located within a quarter of a degree of their true 

 geographical position on the plate, and, with care, errors of over 

 five miles ought not to occur. 



In figure 6 several places are shown as they were located on 

 a I4 cm (5^ inch) diameter, engine divided plate, from the fol- 

 lowing data : 



Greenwich 00° 00' 51° 23' N. 



San Francisco 122 25 W., 37 47 N. 



Honolulu 158 00 W., 21 30 N. 



Northern Luzon 121 00 E., 19 00 N. 



M 105 00 E., 52 30 N. 



* The methods of making the projection have been given by the writer in 

 an earlier communication. Loc. cit. 



