We have no time, just
now to draw diagrams, but, if I express myself clearly, you will no
doubt easily catch the general principle."
"Go ahead!" answered Ardan. "Anything but Algebra."
"We want no Algebra now," said Barbican, "It can't enable us to find
principles, though it certainly enables us to apply them. Well. The Sun
at a certain altitude shines on one side of a mountain and flings a
shadow on the other. The length of this shadow is easily found by means
of a telescope, whose object glass is provided with a micrometer. This
consists simply of two parallel spider threads, one of which is
stationary and the other movable. The Moon's real diameter being known
and occupying a certain space on the object glass, the exact space
occupied by the shadow can be easily ascertained by means of the movable
thread. This space, compared with the Moon's space, will give us the
length of the shadow. Now, as under the same circumstances a certain
height can cast only a certain shadow, of course a knowledge of the one
must give you that of the other, and _vice versa_. This method, stated
roughly, was that followed by Galileo, and, in our own day, by Beer and
Maedler, with extraordinary success.
Pages:
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308