A third method--to measure the mountain
profile directly by means of the micrometer--is evidently applicable
only to altitudes lying exactly on the lunar rim."
"That is clear enough," said Ardan, "and another point is also very
clear. In Full Moon no measurement is possible. When no shadows are
made, none can be measured. Measurements, right or wrong, are possible
only when the solar rays strike the Moon's surface obliquely with regard
to the observer. Am I right, Signor Barbicani, maestro illustrissimo?"
"Perfectly right," replied Barbican. "You are an apt pupil."
"Say that again," said Ardan. "I want Mac to hear it."
Barbican humored him by repeating the observation, but M'Nicholl would
only notice it by a grunt of doubtful meaning.
"Was Galileo tolerably successful in his calculations?" asked Ardan,
resuming the conversation.
Before answering this question, Barbican unrolled the map of the Moon,
which a faint light like that of day-break now enabled him to examine.
He then went on: "Galileo was wonderfully successful--considering that
the telescope which he employed was a poor instrument of his own
construction, magnifying only thirty times. He gave the lunar mountains
a height of about 26,000 feet--an altitude cut down by Hevelius, but
almost doubled by Riccioli.
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