To make them, they had telescopes which they now began to employ with great advantage.

To regulate and investigate them, they had the best maps of the day.
Whilst occupied in this silent work, they could not help throwing a short retrospective glance on the former Observers of the Moon.
The first of these was Galileo.

His slight telescope magnified only thirty times, still, in the spots flecking the lunar surface, like the eyes checkering a peacock's tail, he was the first to discover mountains and even to measure their heights.

These, considering the difficulties under which he labored, were wonderfully accurate, but unfortunately he made no map embodying his observations.
A few years afterwards, Hevel of Dantzic, (1611-1688) a Polish astronomer--more generally known as Hevelius, his works being all written in Latin--undertook to correct Galileo's measurements.

But as his method could be strictly accurate only twice a month--the periods of the first and second quadratures--his rectifications could be hardly called successful.
Still it is to the labors of this eminent astronomer, carried on uninterruptedly for fifty years in his own observatory, that we owe the first map of the Moon.