217 
1831.] On Shading Mountain Land. 
the surface of the ground, as it falls upon the plane’ in which the eye is supposed 
to he situated. 
On the horizontal plane the light falls perpendicularly, and is thrown back, of 
course, in the same path. At 45° of inclination in the surface, the light is thrown 
off in a direction parallel to the horizon, and can never return to the plane of the 
eye. At any intermediate angle between these two, the light is reflected so as to 
fall upon that plane more or less obliquely, and the pencil will illuminate a larger 
or a smaller space upon the plane in which the eye is supposed to be situated, ac- 
cordingly, as it may fall with a greater or less degree of obliquity : and conse- 
quently the intensity of the reflected light in that plane will decrease as the poition 
illuminated by the pencil shall increase. 
The following table is calculated accordingly. 
No. 
Ink. 
Water. 
Angle of Inclination. 
1 
1 
9 
16°47 
2 
2 
8 
22°12.5 
3 
3 
7 
2b 39.5 
4 
4 
6 
28 7.5 
5 
5 
5 
30 
6 
6 
4 
31 29 
7 
7 
3 
32 41 
8 
8 
2 
33 41 
9 
9 
1 
34 32 
■vw.uuo lie a^cUUSl lb . viiv, o 
declivity are not indicated with sufficient uniformity ; as for instance, the shades 
representing slopes to 28°, are included in four parts of ink ; for the next six and a 
l'alf degrees from 28° to 34°. 5, five more parts of ink are allowed, and but onepait 
ink is left to represent the remaining 10°.5, so that the differences of inclination, 
in the greater declivities, are to be distinguished but by very trifling variations in the 
tint. But. in fact, few draughtsmen, except the Germans, ever trouble their heads 
to the intensity of the light as it falls on the ground, or on the plane of the eye, 
niter reflection ; nor is it essential that they should. The object is simply, that the 
degree or depth of shade should represent a certain degree of inclination in the sur- 
hce of the ground ; and the clearest and most intelligible manner in which to regulate 
licit degree or depth of shade, is certainly to make a conventional arrangement, that 
the parts of ink, speaking with reference to the twenty cups of ink and water, shall 
la* applied in the direct ratio of the increase of declivity. This is the common prac 
’‘fe with all English draughtsmen who are not theorists ; and it has the arh antaga 
°f being the plainest and least complicated of all the methods which have been 
devised. Even those who aim at exhibiting, with absolute precision, the measured 
inclinations of the ground, may use it with as much advantage as that founded upon 
l*e intensity of the direct illumination. Here follows a table 
No. 
Ink. 
Water. 
Inclination. 
1 
0 
10 
0 
2 
1 
9 
4.5 
3 
2 
8 
9 
4 
3 
7 
13.5 
5 
4 
6 
18 
6 
5 
5 
22.5 
7 
6 
4 
27 
8 
7 
3 
31.5 
9 
8 
2 
36 
10 
9 
1 
40.5 
11 
10 
0 
45 
