Kepler's Laws of Planetary Motion: 1609–1666

Synopsis

Historians of seventeenth-century science have frequently asserted that Kepler's laws of planetary motion were largely ignored between the time of their first publication (1609, 1619) and the publication of Newton's Principia (1687). In fact, however, they were more widely known and accepted than has been generally recognized.

Kepler's ideas were, indeed, rather slow in establishing themselves, and until about 1630 there are few references to them in the literature of the time. But from then onwards, interest in them increased fairly rapidly. In particular, the principle of elliptical orbits had been accepted by most of the leading astronomers in France before 1645 and in England by about 1655. It also received quite strong support in Holland.

The second law had a more chequered history. It was enunciated in its exact form by a few writers and was used in practice by some others without being explicitly formulated, but the majority, especially after 1645, preferred one or another of several variant forms which were easier to use but only approximately correct. The third law attracted less interest than the others, chiefly perhaps because it had no satisfactory theoretical basis, but it was correctly stated by at least six writers during the period under review.

Between about 1630 and 1650 Kepler's Epitome Astronomiae Copernicanae (in which all three laws were clearly formulated) was probably the most widely read work on theoretical astronomy in northern and western Europe, while his Rudolphine Tables, which were based upon the first two laws, were regarded by the majority of astronomers as the most accurate planetary tables available.

Kepler's work certainly did not receive all the recognition it deserved, but the extent to which it was neglected has been much exaggerated.