Notes on Map Projections. B27 
the highest grasp and compass.* This general problem has led 
to the following modes of projections, (all technically, though 
some quite incorrectly so called,) each of which has been used, 
maps or charts. This classified synopsis will serve to show more 
precisely the relative value and precise character of the polyconic 
projection. 
thographic. 
Ctass L—Perspective pro- } Globular, or equidistant. 
jections on planes, Stereographic. 
Gnomonie, or central. 
By a tangent cylinder. 
Crass Il—Developed per- [ae a secant ipllbelat, 
spective projections, 183 a tangent cone. 
y a secant cone. 
Cassini’s. 
Ctass IIL—Projections by | Flamstead’s. 
developing elements, ‘} Bonne’s, or the modified Flamstead’s. 
Polyconic, (U. 8. Coast Survey.) 
The flat chart, with equal latitude degrees. 
Crass TV. —Projections cn | The flat chart, with latitudes radius X sine of latitude. 
e arbi-+ D . 
formed to som e Lorgna’s. 
trary condition, Ptolemy’s modified conic, 
Mercator’s. 
CLASS I. 
the projected hemisphere are very much crowded. 
Tn the globular or equidistant projection, originated by La 
Hire, the eye is placed at a distance from the centre of the earth 
= Radius + sine 45° = (1+) radius. The plane of projec- 
* Reference on this subject may be made with advantage to the following general 
treatises : Puissant, “Traité de Topographie,” 1805; Henry, “Memoire sur la pro- 
jection des Cartes,” 1810: * ial du de la Guerre? tome ii and iv; La 
Precis mique.” in “ Pinkerton’s Geography ;” Barbié Dubocage, an 
i = cer ire i et Militaire” Francoeur’s “ Traité de 
buch ;” Mayer's “ Practical Geometry, 
