a Notes on Map Projections. 
zone being-of uniform width, occupies a constant breadth along 
its entire developed length, and consequently the area of the 
plane projection is exactly equal to that of the spheroidal surface 
thus developed. This demonstration applies directly to an analo- 
gous plane development of the surface of all supposable surfaces 
of revolution, be the generating meridian curve what it may, and 
even though the generatrix be one of double curvature. The 
meridians of the developed spheroid are traced through the same 
points of the parallels in which they before intersected them. 
They all cut the parallels obliquely, and are concave towards the 
central meridian. ‘Thus, while each quadrilateral between par- 
allels and meridians contains the same area and points after de- 
velopments as before, the form of configuration is considerably 
distorted in receding from the central meridian, and the obliquity 
of intersections between parallels and meridians grows to be 
highly unnatural. 
Bonne’s, or the modified Flamstead’s projection, to a great 
extent obviates this defect. It is the same as Flamstead’s, ex- 
cept that the elementary zones, instead of being developed on 
right lines, are rolled out on concentric circular ares described 
from the vertex of the cone tangent along the central parallel for 
their common centre. The great importance and wide use 0 
this method induce a more detailed treatment of it under a sub- 
joined heading. 
The polyconic projection, being that for which the Coast Sur- 
vey tables are prepared, will be specially explained further on 1" 
its proper place. 
CLASS Iv. 
The flat-chart projection, with equal latitude degrees, is & rude 
method once much in use*for char T'wo sets of equidistant 
perpendicular lines, composing a series of equal squares, @ 
arbitrarily assumed as parallels and meridians to which all local- 
ities were referred by latitudes and longitudes. Hence resulted 
