50 Meteorological Sketches. 
n— | : 
) Poi If therefore the octahedron mP and its interaxes be project- 
ed, and these interaxés be ad a by a portion of their length ex- 
pressed in the fraction, — —— > they will equal the interaxes of the 
a 
octagonal pyramid mPn. This solid may then be projected by con- 
necting the extremities of these interaxes, with the extremities of 
the horizontal axes, and joining all the angles of the octagonal base 
thus formed, with the extremities of the vertical axis. 
25. Tetraxonal system.—The dihexagonal pyramid (fig. 126.) 
may be projected in the same manner as the octagonal pyramid just 
described ; that is, by increasing the interaxes by a_ portion equal to 
n—1 
n+l 
and connecting the angular points of the base thus projected, with | 
the extremities of the vertical axis. 
The scalenohedron (fig. 116.) mR” admits of a similar construc- 
tion with the rhombohedron mR. ‘The only variation required, is 
to multiply the vertical axis, by the number of units in m, after the 
pots E and E’ in the rhombohedron mR have been determined ; 
then connect the points E, or the points E’, with one another and 
with the extremities of the vertical axis. 
— 17? uniting the points thus determined with the horizontal axes, 
e 
Art. IV.— Meteorological Sketches ; by an Observer. 
[Prepared for the 13th edition of the American Coast Pilot.] 
Tue science of Meteorology is not only interesting to the philo- 
sophic observer, but the natural phenomena of which it takes cog- 
nizance, are such as daily affect the interest and comfort of every 
-member of the human family. But to no class of persons are these 
phenomena, as exhibited in various parts of the world, of so much 
practical importance as to the members of the nautical nelession A 
competent knowledge of these exhibitions, or of geographical mete- 
orology, is therefore an important element of that varied knowledge 
which is acquired by the skillful navigator. 
General View of the Atmosphere. 
The transparent aerial fluid which surrounds our globe, and which 
we denominate the atmosphere, forms a comparatively thin stratum 
