Apart from statics, about which I shall say nothing, there were three chief centres of interest in mechanics in the 1660's:

(1) the motions of pendulums;

(2) the laws of motion;

(3) the free fall of heavy bodies and the motion of projectiles.

In the first the influence of Huygens was dominant; I have placed it so because it was of very lively contemporary concern. The second area of interest descended partly from Galileo and partly from Descartes; the third from Galileo alone. Perhaps one should consider adding a fourth area, the investigation of central forces, but this in fact did not attract much attention as yet.

The slow emergence of Dalton's chemical atomic theory has long been a considerable puzzle to historians of science The lengthy delay between Dalton's early work on mixed gases (September 1801) and particle weights (September 1803) and the eventual publication of the first part of his New System of Chemical Philosophy (June 1808) has called forth a variety of explanations. It is now more than half a century since A. N. Meldrum stressed

“…the efforts Dalton had to make, in order to arouse attention to the importance of his ideas regarding atoms. For some nine years (1801-1810), if not longer, he endeavoured to spread abroad his ideas, both by private communications and publicly, by his writings and by lectures in various parts of the country…

“Dalton's chemical theory was formed by the 6th September 1803, and he proceeded forthwith to extend and apply it, and make it known in every direction…”

And though Meldrum's view is now no longer accepted, no systematic and detailed account of Dalton's activities over these years is available to replace Meldrum's assertions.

During his long life Alexander von Humboldt (1769–1859) was mainly connected with three European countries: Germany, France and Russia; nevertheless, he had many scientific and personal relations with England, with British scientists, and with other distinguished citizens of Great Britain. Thus Humboldt's life provides an interesting example of international scientific relations in the nineteenth century. The present paper offers a brief account of this universal and versatile scientist's relations with England in particular.

The atomic theory of Dalton implied that there were more than 30 different kinds of matter, the chemical elements. William Prout (1815) was the first of a long line of distinguished speculators who sought to show, by argument and experiment, that this diversity overlay a more fundamental unity. Contrary to a common opinion, this was not an eccentric and unpopular movement, but involved many of the great names of nineteenth-century chemistry; and some of their speculations have proved to be very near the mark. It may be that this strong current of well-informed speculation enabled the discoveries of cathode rays and of radioactivity (which provided the first real evidence of the complexity of the atom) to be integrated into the body of science with such remarkable rapidity.