An account of the astronomical discoveries of Kepler : including an historical review of the systems which had successively prevailed before his time / By Robert Small.

  • Robert Small
Date:
1804
Catalogue details

Licence: Public Domain Mark

Credit: An account of the astronomical discoveries of Kepler : including an historical review of the systems which had successively prevailed before his time / By Robert Small. Source: Wellcome Collection.

Provider: This material has been provided by the Harvey Cushing/John Hay Whitney Medical Library at Yale University, through the Medical Heritage Library. The original may be consulted at the Harvey Cushing/John Hay Whitney Medical Library at Yale University.

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    such immense magnitude, that the earth, in com- First mo- parison with it, was to be considered only as a sin- tion.ordi- gle point: and, by the constant rotation of this imjon/^ expanse upon its axis, the whole phenomena of the diurnal revolution, called the first motion, were explained. 2. But in attendino; to the circumstances of the diurnal revolution, it was discovered that seven of the celestial bodies, to wit, the Sun, the Moon, Mercury, Venus, Mars, Jupiter, and Saturn, though constantly carried round the earth in the course of the diurnal revolution, neither described their circles with the same accuracy as the rest, nor in the same precise portion of time. On mark- ing the points of the horizon, where on any parti- cular day they rose and set, they were always found after some interval to rise and set at different points, more to the north, or to the south : and, in the same manner, the points where they crossed the meridian were also observed to vary, though within certain limits ; and their transits over it to be made at unequal distances, both from the zenith and from either pole. Those diurnal circles were seldom great circles of the sphere : they were ra- Peculiar ther a perpetual spiral than a series of circles, and motions of resembled a thread regularly wound about a cylin- ^^^1 todies] der, and continually passing and re-passing be- tween its extremities. One of the most early dis- tinctions, made among the celestial bodies, was actually taken from the different velocities with which they performed their diurnal revolution. The stars, afterwards called fixed, were considered as the swiftest of all: the Sun, Mercury, Venus, Mars, Jupiter, and Saturn, were conceived to move with somewhat less rapidity : and the Moon was B '1 reckoned