62 PHILOSOPHICAL TRANSACTIONS. [aNNO 1736. 



are apt to receive wrong notions and prejudices from them; at least they cannot 

 be rightly and easily instructed by them. 



To obviate this inconvenience, geographers have contrived the terrestrial 

 globe, on which they endeavour to delineate all the parts of the earth's surface 

 in their natural state, as to longitude, latitude, distance, bearing, magnitude, 

 &c. which being a true and genuine representation of the whole superficies of 

 the earth, as far as it is yet known, is the best adapted for conveying just no- 

 tions to young minds, and for preventing all false conceptions and preposses- 

 sions. After the first rudiments of geography have been imbibed from hence, 

 they will be then prepared for the use of plain maps; and they will afterwards 

 find, that large projections of particular countries, kingdoms, and provinces, 

 in piano, will be of excellent service for their further improvement in this useful 

 and necessary science. Nor will they now be in any danger of being misled 

 by such maps, though they are not so just and niatural representations of the 

 terrestrial globe. 



Now the same conveniencies that may be derived from the whole globe, may, 

 in proportion, be had from any notable portions of it; as a hemisphere, a 

 quadrant, a sextant, an octant, or other part. But with this advantage besides, 

 that these partial spherical maps will not only be much less cumbersome, and 

 more manageable than a whole globe, but may be made much more accurate 

 and particular, as they are capable of being formed to a much larger diameter, 

 than a globe can conveniently be made to. The maps may first be printed on a 

 plane, as is usual in the common globes, and then pasted on thin convex shells 

 of pasteboard, formed to the intended radius. The forming of these spherical 

 coats of pasteboard will be a matter of no great difficulty, even to as large a 

 diameter as shall be desired ; but the chief art will be required in projecting 

 the maps in piano, after the simplest and exactest manner, so as they may adapt 

 themselves, with as little error as possible, to a spherical surface. For a 

 plane surface cannot be converted into a spherical surface without some error. 

 The best method of doing this, with the least possible error, may be as 

 follows. 



Instead of the usual slips or gussets, as is the manner of globe-makers, which 

 are comprehended between two meridians at some distance, and are formed only 

 tentatively and mechanically, without the help of any just theory, we may divide 

 the whole spherical surface into parallel portions, or zones; that is, into parts 

 terminated by two parallels to the equator, at the distance suppose of 10 degrees. 

 As if the first of these portions, or zones, were at the equator itself, and ex- 

 tended to 5 degrees of latitude on each side of that circle; the second zone 

 would be at the parallel of 10 degrees of latitude, and would extend to 5 de- 



