The Life of Dr. Robert Hooke.

...Moon upon the air in its passage by the meridian—were true or not. At this time, I have heard Mr. Hooke say it was first observed that the height of the mercury in the barometer did not conform itself to the moon’s motion, but to the varying gravitation of the air, as has been sufficiently verified since. Yet in a French treatise printed in Paris Treatises on the Equilibrium of Liquids, etc. 1664. several years after this observation at Oxford, the discovery of the gravitation of the air is attributed to Monsieur Pascal, deduced from several experiments made around the year 1650 at Clermont in Auvergne by Monsieur Perier, at Paris by others, and at Stockholm by Monsieur Des Cartes and Monsieur Chanute. If it is as related there, and the conclusions drawn from the experiments are as mentioned in that tract, it is strange they were not applied to the use of so beneficial an instrument sooner, which I do not find to have been the case until after this observation at Oxford.

By the persuasion of Dr. Seth Ward, afterwards Bishop of Salisbury, about 1656, he applied himself more particularly to the study of astronomy. Around 1658 or 1659, he says, "I contrived several astronomical instruments for making observations both at sea and land, which I afterwards produced before the Royal Society."

Some of these, I suppose, are the instruments mentioned hereafter in his astronomical lectures, where I have endeavored to retrieve as many as I could, partly from rough drafts, partly from old models, and some from verbal descriptions where both those aids were lacking. How I have succeeded in this, I leave to the candid reader’s judgment.

Much about this time (as he says) he contrived the circular pendulum and its use for continuing the motion of another pendulum, which he later showed to the Royal Society in 1663. Around this time and afterwards, there are several entries in the journals relating to the circular pendulum as being his. A movement to this purpose is described in his Animadversions on the Machina Coelestis, page 68, printed in 1674.

In the year 1660, the most illustrious Royal Society was founded. For a full account of its institution, the reader is referred to the right reverend and learned Dr. Sprat’s history thereof, published in 1667. I shall only observe the occasion and time when Mr. Hooke was introduced into their service as curator. Soon after the beginning of the Royal Society, namely about April 1661, a debate arose in the Society, occasioned by a small tract printed in 1660 about the cause of water rising in slender glass pipes higher than in larger ones, and that in a certain proportion to their bores. This discourse was written and published by Hooke; the explanation of this difficult phenomenon made him more regarded. The sum of his reasonings upon this subject he published afterward in his Micrographia, observation the 6th, in which there are several very curious and then-new remarks and hints as to the nature of fluidity and gravity, which the latter is further prosecuted in his Treatise of Springs, with other excellent subjects, to which the inquisitive are referred for more ample satisfaction.