The same thing was remarked here as at Exeter in 1586 that those who sat on the side of the Court nearest to the dock were most attacked by the infection[166]. When the cases of fever began to occur, after the usual incubation of “a week or ten days,” there was much fear of the infection spreading, so that many families, it is said, retired into the country[167]. But Pringle wrote on 24 May, “However fatal it has been since the Sessions, it is highly probable that the calamity will be in a great measure confined to those who were present at the tryal[168];” and Justice Foster gives no hint of anyone having taken the fever who was not present in court. The tragedy of gaol-fever at the Old Bailey in 1750 secured increased attention to the subject of scientific ventilation. The great bar to fresh air indoors throughout the 18th century was the window-tax. It bore particularly hard on prisoners, for the gaolers had to pay the window-tax out of their profits, and they naturally preferred to build up the windows. Scientific ventilation of gaols was something of a mockery in these circumstances; but it is the business of science to find out cunning contrivances, and ingenious ventilators were devised for Newgate, the leading spirit in this work being the Rev. Dr Hales, rector of a parish near London, and an amateur in physiology at the meetings of the Royal Society. A ventilating apparatus had been erected at Newgate about a year before the fatal sessions of 1650, but it does not seem to have answered. It consisted of tubes from the various wards meeting in a great trunk which opened on the roof. A committee of the Court of Aldermen in October 1750 resolved, after consulting Pringle and Hales, to add a windmill on the leads over the vent, and that was done about two years after. Pringle, who inspected the ventilator on 11 July, 1752, says that a considerable stream of air of a most offensive smell issued from the vent; and it appeared that no fewer than seven of the eleven carpenters who were working at the alterations on the old ventilator caught gaol-fever (of the petechial kind), which spread among the families of some of them[169]. Pringle and Hales were of opinion that the wards furnished with tubes were less foul than the others; and they claimed, on the evidence of the man who took care of the apparatus, that only one person had died in the gaol in two months, whereas, before the windmill was used, there died six or seven in a week[170]. But Oglethorpe had claimed an improvement of the same kind at the Marshalsea in 1729 merely from having the prisoners saved from hunger; and Lind, who was a most matter-of-fact person, did not think that the ingenious contrivances for ventilation had answered their end[171].