“That calces do not become metals merely by parting with the air they contain, is evident from my experiments on heating them in contact with inflammable air, in which the inflammable air, or some necessary part of it, is undoubtedly absorbed; and though a little moisture be deposited in the process, it may well be supposed to be that which in conjunction with phlogiston constituted the inflammable air. And what can the other principle that is absorbed by the calx be but the same thing which, when united to water, is recovered again from the metal and found to be inflammable air having all the same properties with that which was employed in the revival of it. Metals therefore are not simple substances, but consist of their calces, and something else which they take from inflammable air. And as the same may also be taken from any combustible substance, it corresponds exactly to Stahl’s phlogiston, and therefore the doctrine of it is confirmed by these experiments; that is, we must still say that in all combustible substances there is a principle capable of being transferred to other substances, which when united to the calces of metals makes them to be metals, and which, united to oil of vitriol (deprived of its water) makes it to be sulphur.” Thus was the ingenious man effectually entangled in his errors, his ingenuity helping him to deceive himself by evading the force of truth. To err is human. If Priestley saw through a glass darkly, and but dimly discerned the truth, he at least strove, so far as in him lay, to reach the light. Posterity forgives, and may well forget, his errors in grateful recognition of the many noble services he rendered to our common humanity, and in humbling recollection of the suffering and sacrifice with which those services were requited. FOOTNOTES [1]The Gregorian Calendar was not adopted in Great Britain until 1751. In 1752 eleven days were left out of the Calendar, September 3rd being counted the 14th. The change of style probably accounts for the confusion in the various dates of Priestley’s birth given by different writers. In Chalmers’s _General Biographical Dictionary_ the date is given as March 18; in Allen’s _American Biographical and Historical Dictionary_ and in Thomson’s _History of the Royal Society_ as March 24; Corry, in his _Life of Priestley_, gives March 24; Hoefer, in his _Histoire de la Chimie_, gives March 30, probably following Dumas’s _Philosophie de Chimie_; Cuvier, in his _Eloge_, says that he was born near Bristol in 1728! In a letter to Wedgwood, dated March 23, 1783, Priestley says in a postscript “This day I complete my half century.” [2]T. Wemyss Reid, _Memoir of John Deskin Heaton_, p. 7 _et seq._