108 ASTRONOMY. 
circle of that place divided into twenty-four hours. Although at the end 
of December the earth is nearest the sun, yet at that time in the northern 
hemisphere, the heat is less than at any other. The reason of this lies in 
the fact of the short days and long nights, as well as that the sun’s rays fall 
very obliquely on the earth, traversing a longer path through the atmo- 
sphere, and consequently losing much of their heating power. At the 
beginning of July, on the contrary, although then the earth is at its greatest 
distance, the temperature of the northern hemisphere <s greatest, on account 
of the long days and short nights, and the great altitude of the sun at noon. 
This, of course, depends upon the declination of the sun north or south from 
the equator. This declination of the sun for the first day of every month, is 
given in pl. 8. The great inner circle contains the division of the year into 
days and months, and enables us, by drawing a straight line to any point of 
this circle, to find the situation of the earth on the day corresponding to the 
point. The external circle, on the contrary, is divided into twelve equal 
arcs, of which each one answers to a sign (30 degrees) of the ecliptic. It 
must not be forgotten, however, that owing to the precession of the equi- 
noxes, these signs no longer correspond to the constellations of the same 
name, so that now the sign Pisces corresponds to the constellation Aries, 
the sign Aries to the constellation Taurus, &c. It is further evident from an 
inspection of the plate. that if the earth at the beginning of spring, summer, 
autumn, and winter, should be in the signs Aries, Cancer, Libra, and Capri- 
cornus respectively, then the sun, as being always directly opposite in the 
ecliptic, will be in the signs Libra, Capricornus, Aries, and Cancer. 
By properly combining the preceding with sections 27, 28, which are 
devoted principally to an explanation of the theory of the seasons, and par- 
ticularly of the daily and yearly motion of the sun, it will not be difficult to 
obtain a perfect idea of all the phenomena occurring in the course of a 
year, over the whole surface of the earth. On account of the great im- 
portance of this subject, it may be remarked further, that the changes of 
days and nights, as also of the seasons, may be very easily represented by 
means of a Tellurium, or by means of a terrestrial globe, with a little simple 
additional mechanism. 
The inner space of pl. 8, is employed to represent the orbits of the two 
inferior planets, Mercury and Venus, in their proportional size, shape, and 
eccentricity. The accompanying figures are readily intelligible without 
further explanation. 
27. The sun is stationary! It is incredible that so enormous a body as the 
sun should have three different motions at the same time. Accurate 
observations have shown that the earth moves about its axis from west to 
east, once every day, by means of which the daily apparent motion of the 
heavens, as well as of the sun, from east to west is produced. It is further- 
more only apparently, not really, that the sun in the course of a year moves 
around the earth from west to east in an ellipse termed the ecliptic (pl. 9, 
fig. 3, LCD), making an angle with the equator of 23° 27’... This inclination, 
termed the obliquity of the ecliptic, combined with the revolution of the 
earth, explains the apparent motion of the sun, both towards the north and 
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