The Corporation of London, moved thereto by a letter from the Lord Chief Justice, and not unnaturally alarmed themselves at the ravages of a pestilence which spared neither Lord Mayor nor aldermen, set about inquiring into its origin. A committee was appointed for this purpose in October, 1750, five months after the last outbreak, and their instructions were to ascertain “the best means for procuring in Newgate such a purity of air as might prevent the rise of those infectious distempers.” ... The committee consulted the Rev. Dr. Hales and Dr. Pringle, F.R.S.,[183] the latter of whom subsequently published a paper in the ‘Transactions of the Philosophical Society,’ containing much curious information concerning the disease. The remedy suggested by Dr. Hales, and eventually approved of by the committee, was to try further the ventilator which some time previously had been placed upon the top of Newgate. Nothing less than the reconstruction on an extended plan of the prison, which was acknowledged to be too small for its average population, would have really sufficed, but this, although mooted, had not yet taken practical shape. The existing ventilator was in the nature of a main trunk or shaft, into which other air-pipes led from various parts of the prison. But these were neither numerous nor effective, while there was no process of extraction or of obtaining an up-draught. To effect this a machine was erected upon the leads of Newgate with large arms like those of a windmill. The plan was fully approved of by the Court of Aldermen, but its execution was delayed. At length, in July, 1752,[184] Dr. Pringle heard that a portion of the machine was completed and in working order, and went to inspect it, accompanied by other medical men. “Having visited several of the wards,” he says, “we were all of us very sensible that such as were provided with ventilating tubes were much less offensive than the rest that wanted them.” The air of the whole gaol they thought was distinctly improved. Some of the wards indeed were so free from the smell peculiar to such places that Dr. Pringle felt persuaded that if the design was completed, and persons appointed to regulate the sliders of the tubes, and keep the machine in order, the usual evil effects of overcrowding in gaols might be in a great measure if not wholly prevented in Newgate.