PHYSICAL ASTRONOMY. 147 
65. Heteroscii (érzg0-cx101), or one-shadowed, are those inhabitants of. the 
earth whose shadows among themselves always fall in the same direction ; 
in an opposite direction, however, to the inhabitants of the opposite hemi- 
sphere. Consequently, the inhabitants of the temperate zones are one- 
shadowed ; the shadows in the north temperate zone falling north, those in 
the south temperate zone, south. 
The inhabitants of the frigid zones acquire the name of Periscii (égi-sx101), 
at the time during which the sun remaining above their horizon causes their 
shadows to move in a circle around them in the space of 24 hours. 
Amphiscii (augi-cxo), or double-shadowed, are those inhabitants of the 
tropics who for one half of the year have their shadows directed towards 
the south, and for the other half towards the north. The cause of this lies in 
the fact of the latitude being less than the obliquity of the ecliptic. At any 
place whose latitude is, for instance, 17° north or south, a body will cast ne 
shadow at all at noon of the day, when the declination of the sun is likewise 
17° north or south. For this reason the Amphiscii are then termed Ascii 
(2-001), or shadowless. The inhabitants of the equatorial line itself will be 
shadowless on the 21st of March and 23d of September, since on these days 
the sun stands in the celestial equator. It has, consequently, then no decli- 
nation, and the inhabitants of the line have no latitude. 
66. It is not absolutely impossible that the sun may be habitable, as the 
black places which are seen in the middle of the sun’s spots represent, 
perhaps, not the true nucleus of the sun, but only an obscure atmosphere 
similar to our own. The inhabitants of the sun, therefore, undazzled by the 
plercing light of the external solar surface or photosphere, and protected from 
its excessive heat, may live, ignorant, however, of the alternation of day and 
night. Neither can they os anything of seasons, since they are sur- 
rounded on all sides, and at all times, by the sources of heat and light. They 
can thus know nothing of the existence of the planets, moons, and comets ; 
and can perceive the starry heavens in their beauty only through the open- 
ings which those violent agitations in the sun’s photosphere sometimes 
produce. 
67. Although Mercury receives an illumination from the sun almost seven 
times greater than that of our earth, the heat thus produced may be very 
greatly tempered by the numerous high mountains with their long shadows, 
the rapid alternation of the seasons, and the probably very rare atmosphere. 
In this manner an alleviation of temperature may result, which will without 
difficulty admit of this planet’s being habitable. 
Certain phenomena must take place in the climate and seasons of Venzs 
which hardly admit of a comparison with ours. A day of Venus is very 
nearly equal to one of the earth, but it is very different ‘with respect to the 
seasons, if we assume, as established, that the axis about which Venus 
rotates daily is inclined to its orbit at an angle of nearly 72°, and that thus 
the obliquity of her ecliptic is nearly three times that of the earth. It is 
well known that the seasons are determined by the obliquity of the ecliptic, 
and that, consequently, a much greater obliquity than that of our earth must 
necessarily involve a corresponding influence upon the temperature, and 
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