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Investigations and Writings of Baron Humboldt. 207 
the equator (whence it follows that it is only at places which 
are within the distance of 233° from the equator that the sun ac- 
quires a perpendicular position, and can exercise its greatest 
heating power), it was assumed that the reciprocal inclination 
of the two planes had formerly been different. It might of 
course have been either greater or smaller, and consequently 
two extreme cases are possible, which serve as the explanation 
of all the remaining intermediate ones. The planes of the 
ecliptic and the equator could either at one time have been 
perpendicular to each other, or they could have been identical. 
In the first case the sun would stand perpendicularly over 
each point of the earth’s surface successively, and twice a year, 
and it would do so over the poles themselves, and would thus 
produce at each point a tropical summer ; but it would also, 
upon the same supposition, not rise at all during a certain 
period of the year at any part of the earth’s surface, except 
only at the equator. All these places therefore would have si- 
multaneously a more or less continued real polar winter. Thus 
this division of the seasons would by no means correspond with 
the nature of our tropical climates. But, supposing that the 
plane of the ecliptic was the same with that of the equator 
(as was considered probable by the ancients, who thought that 
this cause had produced the condition of perpetual spring 
which they supposed to have primarily existed), we would of 
course have had the sun visible at the equator from all points 
of the surface of the earth ; day and night would thus have 
been of equal length in all portions of the earth (with the 
exception of the poles, where there would have been perpetual 
twilight), and every distinction of season would have ceased. 
Under such circumstances the sun with us would never rise 
higher than 373° above the horizon, while at present it rises 
to 61° in summer ; we should throughout the whole year have 
the low temperature of our equinoctial periods, the more 
northern localities would be constantly dreary, and, even in 
the tropical zone, its products would flourish at comparatively 
much smaller distances from the equator than at present. 
Hence it is clear that the climate of earlier periods cannot 
be explained by an altered position of the sun in relation to 
the earth. The assumption of such a change of position is so 
