5. The Tartars _Sien pi_, who came from the confines of _Leao tong_ and Mongol or Mogol Tartary, had hords named _To pa_. One of these hords made themselves masters of Tartary _Leao tong_, and of several northern provinces of China. This Tartar power has the Chinese name of _Ouey_. It has produced several great princes. The year of Christ 386 is reckoned the first of that dynasty[153], which reigned above 180 years. I do not know why the reigning dynasty has not placed the name of any of these emperors in the _Ti ouang miao_. 6. If we suppose, first, that all the books of the history of China should be lost, or the contents of them should not be known in Europe; and secondly, that the catalogue of the emperors, who are mentioned in the _Ti ouang miao_, should fall into the hands of some European critics; it is probable, that such a catalogue would occasion many false reasonings with relation to the succession of the emperors, who have reigned in China. XCVII. _An Attempt to improve the Manner of working the Ventilators by the Help of the Fire-Engine. In a Letter to_ Tho. Birch, _D. D. Secret. R. S. from_ Keane Fitz-Gerald, _Esq; F.R.S._ [Read June 8, 1758.] SIR, THE reverend and ingenious Dr. Hales, from whom mankind has received such benefit by his useful application of ventilators, being inclined to extend its use to those, who work in mines at great depths under ground, where the lives of many are lost by damps and noxious vapours, occasioned by the want of a free circulation of air; and finding by experience, that ventilators worked by wind do not operate above one third part of the year, and in calm hot weather, when most wanted, do not operate at all; did me the honour of applying to me for assistance in contriving a machine to work the ventilator, by the help of the fire-engine, which is now generally used in all mines for drawing off the water; and which I have accordingly attempted, and hope it will answer the purpose. As the lever of the fire-engine works up and down alternately, and performs at a common medium about a dozen strokes in a minute, it was necessary to contrive some way to make the beam, tho’ moving alternately, to turn a wheel constantly round one way, and also to increase the number of strokes to fifty or sixty in a minute. The model of a machine for this purpose is composed of four wheels of different sizes, two clicks, three pinions, and a fly; which is put into motion by the part of a wheel fixed to the arch of the lever of the fire-engine. The wheel, which is turned by the lever, or rather moved up and down by it, is loose on its arbor; and likewise one of the rochets, and the wheel next to it. The outside rochet and outside wheel are fixed on the arbor. There are two pinion-wheels fixed on the arbor; one on each side, near the edge of the wheel moved by the lever, which turns them.