in 1791, his house was burned, and he was obliged to escape to London under an assumed name. After some years spent in the charge of a meeting-house at Hackney, he left England for America. His opinions, though by no means uncommon at the present day, were so antagonistic to those of his English contemporaries that he was cut by his Fellows of the Royal Society, and he therefore resigned his Fellowship. And this feeling was in no way lessened by the action of the French Government of the time, which made him a Citizen of the Republic, and even chose him as a member of their Legislative Assembly. Arriving in America in 1795, he was well received, and settled at Northumberland, not far from Philadelphia. There he died in 1804. [Illustration: JOSEPH PRIESTLEY.] In Priestley’s work on gases he employed the form of apparatus which had been used by Mayow a century before. Such apparatus is indeed generally used now: the flasks with bent delivery-tubes, the Wolff’s bottles with two necks, and the pneumatic trough filled with water or mercury were his chief utensils. By means of such apparatus, gases can be collected in a state of comparative purity: they can be easily transferred from one vessel to another, and substances which it is desired to submit to their action can be readily introduced. Scheele, on the other hand, employed less convenient methods: his gases were generally collected in bladders, and their transference to bottles must have been attended with the introduction of atmospheric air. Scheele’s method was to allow a certain amount of gas to escape from the generating flask in order to expel air; an empty bladder was then tied over the neck, and the gas entered the bladder. When he wished to transfer the gas to a bottle, the bladder was tied at some distance from the neck, and its loose open end was secured by a string round the neck of a bottle full of water. The string confining the gas was then untied, and the bottle was inverted; the water ran into the bladder and was replaced by gas. A cork was also enclosed in the bladder, and it was possible to push this cork into the neck of the bottle and re-tie the string which confined the gas; and then, by loosing the string which secured the bottle to the bladder, the full bottle could be conveyed away. This process is obviously a clumsy one, although in Scheele’s hands it yielded splendid results; and the methods which Priestley had borrowed from Mayow have attested their superiority by their survival.