December 10, 1684

De motu corporum in gyrum

Halley reports Newton's De motu treatise to the Royal Society

The Royal Society did not hear Newton's paper that day. It heard Edmond Halley say that Newton had promised to send it.

A curious treatise, described secondhand

At the Royal Society meeting in London on 10 December 1684, Edmond Halley reported that Newton had recently shown him a curious treatise on motion at Cambridge. Newton himself was not present.

Halley said Newton had promised to send the treatise for entry in the Society's register. The meeting asked Halley and Edward Paget to remind him, so that he could secure priority for the work before publication.

What was in it

The work developed mathematical relations between centripetal force and orbital motion: equal areas swept in equal times, the inverse-square force associated with an ellipse's focus, and the period–axis relation now counted among Kepler's laws.

The surviving draft runs to roughly 3,911 Latin words on nine pages, formally structured as four theorems and seven problems. It grew out of Halley's August 1684 visit to Cambridge, where he challenged Newton to demonstrate the orbit produced by an inverse-square central force; Newton supplied a demonstration through Paget in November.

What the register copy did not prove

The tract was sent and entered later, by February 1685. It was not read to the Society on 10 December, and a date written on the later register copy does not prove the copy was physically registered then.

The original manuscript is lost; what survives is a draft and contemporary copies, so even the title De motu corporum in gyrum is not securely that of the lost original. The meeting date is Old Style, corresponding to 20 December 1684 in the Gregorian calendar.

Sources

Researched 23 Aug 2026 5 sources 2 audit passes Traditional date

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

Traditional date. This date is the conventional one, not one fixed by a contemporary record.

What the sources leave uncertain

The meeting date is an English Old Style/Julian date. It corresponds to 20 December 1684 in the Gregorian calendar.
The original manuscript is lost. What survives is a draft and contemporary copies, including a register-book copy; the title De motu corporum in gyrum is not securely the title of the lost original.
The exact relationship among the November demonstration, the treatise Halley saw in Cambridge and the version later registered has long been debated. The meeting record is nevertheless clear that Halley gave an account of a promised tract rather than reading the tract itself.