Franklin, one winter's day passing with a lighted candle out of a warm
room into a cold one, saw that as he held it above his head the flame
was blown outward before him: when he held it near the floor, the
flame was blown into the room. The shrewd observer stood in the
doorway, instead of hurrying out, as most of us would have done,
to save the wasting candle. The warm air in the heated room, he
conjectured, was expanded by the heat, consequently it rose as high as
it could, and made a way for itself out of the room at the upper part
of the doorway, while the heavier cold air from without rushed in
below to fill the vacated space. What if he took the equatorial
regions or great tracts of arid desert for the heated room? The air
over them, subjected by the heat to constant rarefaction, must
rise, must overflow above, and must force the colder air from the
surrounding regions in below. Two sheets of air will thus set in
vertically on both sides, rise, and again separate above. Here was an
explanation of the great, steady, uninterrupted aerial currents which,
at the rate of from fifteen to eighteen miles per hour, sweep the
surface of the Atlantic and Pacific oceans.
Pages:
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196