But nothing of a nature foreign to the duties of my profession engaged my attention while I was at Leeds so much as the prosecution of my experiments relating to _electricity_, and especially the doctrine of _air_. The last I was led into in consequence of inhabiting a house adjoining to a public brewery, where I at first amused myself with making experiments on the fixed air which I found ready made in the process of fermentation. When I removed from that house, I was under the necessity of making the fixed air for myself; and one experiment leading to another, as I have distinctly and faithfully noted in my various publications on the subject, I by degrees contrived a convenient apparatus for the purpose, but of the cheapest kind. When I began these experiments I knew very little of _chemistry_, and had in a manner no idea on the subject before I attended a course of chemical lectures delivered in the academy at Warrington by Dr. Turner[10] of Liverpool. But I have often thought that upon the whole, this circumstance was no disadvantage to me; as in this situation I was led to devise an apparatus, and processes of my own, adapted to my peculiar views. Whereas, if I had been previously accustomed to the usual chemical processes, I should not have so easily thought of any other; and without new modes of operation I should hardly have discovered any thing materially new.[11] [10] Dr. TURNER was a Physician at Liverpool: among his friends a professed Atheist. It was Dr. Turner who wrote the reply to Dr. Priestley’s letters to a philosophical unbeliever under the feigned name of Hammon. He was in his day a good practical chemist. I believe it was Dr. Turner who first invented, or at least brought to tolerable perfection, the art of copying prints upon glass, by striking off impressions with a coloured solution of silver and fixing them on the glass by baking on an iron plate in a heat sufficient to incorporate the solution with the glass. Some of them are very neatly performed, producing transparent copies in a bright yellow upon the clear glass. Dr. Turner was not merely a whig but a republican. In a friendly debating society at Liverpool about the close of the American war, he observed in reply to a speaker who had been descanting on the honour Great Britain had gained during the reign of his present Majesty, that it was true, we had lost the _Terra firma_ of the thirteen colonies in America, but we ought to be satisfied with having gained in return, by the generalship of Dr. Herschel, a terra incognita of much greater extent _in nubibus_. T. C.