Notes on Map Projections. 339 
This method requires much less recourse to the tables than the 
other, and is sufficiently accurate, within a square degree, on a 
cale of +5455. The x and y may often be neglected as insen- 
sible in small projections; but no value of z, which is at all ap- 
preciable on the scale used, should be neglected. he y, for the 
auxiliary parallels, affects the meridian less rapidly, but its palpably 
sensible values should always be used. 
The following quantities are sensible, yet only barely sensible, 
on the scales affixed : 
12 metres on a scale of ~-1-.. 
80 00 
10 “ 6c a ES 
00° 
8 tt te Ero ete dy! 
40 00° 
6or5 * 6 aeine 
3 0.0° 
2 Ts 6 ae 
2 00° 

nd it is peculiarly essential to accurate projections that the hy- 
grometric condition of the paper be kept as uniform as possible 
during all the time that measured distances are being laid down. 
It is often better to mark simply the intersection points by a small 
cross +, and to omit the remainder of the parallels and meridians. 
For plotted points this is also the best indication, if the cross lines 
are stopped on each side of the point, just far enough off to leave 
the dot distinct. 
For drawing parallels and meridian curves, a long, slender, 
flexible ruler of straight-grained cedar, or other compact wood, 
lsemployed. Its cross section is three-sixteenths (,%,) of an inch 
by two sixteenths (#;) of an inch. A specially designed steel 
tuler might be found preferable. ‘There is a small groove on the 
top of the ruler, and its ruling edge is slightly beveled. Leaden, 
Paper-covered, beak weights, of about four pounds weight each, 
are used to hold the ruler in place from point to point. These 
are so shaped as not to incommode the hand in ruling, and each 
has a hooked beak, ending in a knife-edge, turned downwards, 
Which, resting in the ruler groove, throws the main bearing of 
the weight on the ruler, while its small end rests on the paper. 
‘he beak weights in use are five (5) inches long, two and one- 
eighth (24) wide, and two and one-eighth (24) deep, the beak 
being five-eighths (&) of an inch long, and turned down one-fourth 
_(t)inch. The mass of lead is nearer the beak end. Having 
Placed the ruler approximately, it is so adjusted under a beak 
Weight to the first point that the curve will be ruled exactly 
through it. It is then adjusted under a second weight to the 
