Humfrey, an eminent mathematician, was born at Salisbury, May 29, 1675. At his father's request he entered on the study of theology, and was for some years a dissenting minister at Tunbridge, where he married. On the death of his father, however, he was induced to relinquish the clerical profession; and at the persuasion of Mr Whiston and Dr Harris he devoted himself to the more genial study of mathematics. Through the influence of Sir Isaac Newton, he was elected mathematical master in Christ's Hospital, where he continued till his death in 1715.

Ditto was the author of the following treatises:—Of the Tangents of Curves, &c., Phil. Trans. vol. xxiii.; A Treatise on Spherical Catoptries, published in the Phil. Trans. for 1705, from which it was copied and reprinted in the Acta Eruditorum, 1707, and also in the Memoirs of the Academy of Sciences at Paris; General Laws of Nature and Motion, 8vo, 1705. (Wollius commends this work, as illustrating and rendering easy the writings of Galileo, Huygens, and the Principia of Newton. It is also noticed by La Roche, in the Memoires de Litterature, vol. iii. p. 46.) An Institution of Fluxions, containing the first Principles, Operations, and Applications of that admirable method, as invented by Sir Isaac Newton, 8vo, 1706. In 1709 he published the Synopsis Algebraica of John Alexander, with many additions and corrections. In his Treatise on Perspective, published in 1712, he explained the mathematical principles of that art; and anticipated the method afterwards elaborated by Dr Brook Taylor. In 1714 Ditton published his Discourse on the Resurrection of Jesus Christ; and The New Law of Fluids, or a Discourse concerning the Ascent of Liquids in exact Geometrical Figures, between two nearly contiguous Surfaces. To this was annexed a tract to demonstrate the impossibility of thinking or perception being the result of any combination of the parts of matter and motion; a subject much agitated about that time. There was also added an advertisement from him and Whiston concerning a method for discovering the longitude, which it seems they had published about half a year before. This attempt probably cost our author his life. Although approved by Sir Isaac Newton before being presented to the Board of Longitude, and the method had been successfully practised in finding the longitude between Paris and Vienna, the board determined against it. This disappointment, together with some sarcastic lines written by Dean Swift, affected Ditton's health to such a degree that he died in the following year.

In an account of his life, prefixed to the German translation of his Discourse on the Resurrection, it is said that he had published, in his own name only, another method for finding the longitude. This Whiston denied. However, Raphael Levi, a learned Jew, who had studied under Leibnitz, informed the German editor that he well knew that Ditton and Leibnitz had corresponded upon the subject; and that Ditton had sent to Leibnitz a delineation of a machine he had invented for that purpose, and which Leibnitz highly approved of for land use, but doubted whether it would answer on board a ship on account of the motion.