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Observation of a granular structure in cometary nuclei dates far back into the seventeenth century, when Cysatus and Hevelius described the central parts of the comets of 1618 and 1652 respectively as made up of a congeries of minute stars.
This change or libration is of four different kinds, viz. the diurnal libration, the libration in longitude, the libration in latitude, and the spheroidal libration. Galileo discovered the first of these kinds of libration, and appears to have had some knowledge of the second; but the third was discovered by Hevelius, and the fourth by Lagrange.
Between 1594, when he published his Kalendar at Gratz, and 1630, the year of his death, he published no fewer than thirty-three separate works; and he left behind him twenty-two volumes of manuscripts, seven of which contain his epistolary correspondence. The celebrated astronomer Hevelius, who was a cotemporary of Louis Kepler, purchased all these manuscripts from Kepler's representatives.
Number of Kepler's published Works His numerous Manuscripts in 22 folio volumes Purchased by Hevelius, and afterwards by Hansch Who publishes Kepler's Life and Correspondence at the expense of Charles VI. The History of the rest of his Manuscripts, which are deposited in the Library of the Academy of Sciences at St Petersburg General Character of Kepler His Candour in acknowledging his Errors His Moral and Religious Character His Astrological Writings and Opinions considered His Character as an Astronomer and a Philosopher The Splendour of his Discoveries Account of his Methods of Investigating Truth.
Galileo explained the phenomena of the lunar light produced during certain of her phases by the existence of mountains, to which he assigned a mean altitude of 27,000 feet. After him Hevelius, an astronomer of Dantzic, reduced the highest elevations to 15,000 feet; but the calculations of Riccioli brought them up again to 21,000 feet.
Not but that the lunar surface had already been diligently studied, chiefly by Hevelius, Cassini, Riccioli, and Tobias Mayer; the idea, however, of investigating the moon's physical condition, and detecting symptoms of the activity there of natural forces through minute topographical inquiry, first obtained effect at Lilienthal.
He was subsequently elected to the important office of secretary to the Royal Society, and he discharged the duties of his post until his appointment to Greenwich necessitated his resignation. Within a year of Halley's election as a Fellow of the Royal Society, he was chosen by the Society to represent them in a discussion which had arisen with Hevelius.
Regiomontanus and Tycho Brahé proved by their observations that they are situate beyond the moon; Hevelius, Dörfel, &c., made them revolve around the sun; Newton established that they move under the immediate influence of the attractive force of that body, that they do not describe right lines, that, in fact, they obey the laws of Kepler.
The earliest observations did not discover these furrows. Neither Hevelius, Cassini, La Hire, nor Herschel seems to have known them. It was Schroeter who in 1789 first attracted the attention of savants to them. Others followed who studied them, such as Pastorff, Gruithuysen, Boeer, and Moedler.
"We may judge how great was the improvement which these contrivances introduced into the art of observing," says Whewell, "by finding that Hevelius refused to adopt them because they would make all the old observations of no value.
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