462
Leopold — Blahey — Rivatz.
[Book IV.
metvm or the pressure of the atmosphere 29 feet high, out of a well, andthen pressed up 11 feet higher. Another engine of this sort which I putup for a friend about five and twenty years ago, [1719] drew up the water29 feet from the well, and then it was forced up by the pressure of thesteam 24 feet higher,” &c. But these “ improved ” engines differed inreality but little from Savery’s single one, No. 194. Desaguliers furnishedhis boiler with Papin’s steelyard safety-valve; a three-way cock alternatelvadmitted steam into the receiver and water from the forcing pipe to con-dense it: in other respects the engines were much the sarne. Saverymade no provision to secure his boilers from being exploded ; but thesafety-valve was not always a preventive in former tirnes, any more thanat present. “ About three years ago [says Desaguliers ] a man who wasentirely ignorant of the nature of the engine, and without any instructions,undertook to work it; and having hung the weight at the farther end ofthe steel-yard, in Order to collect more steam to make his work the quicker,he hung also a very heavy plumber’s iron upon the end of the steel-yard:the consequence prov’d fatal, for after some time the steam, not being ablewith the safety-clack to raise up the steel-yard loaded with all this unu-sual weight, hurst the boiler with a great explosion, and kill’d the poorman.” Exp. Philos. ii, 489.
In a double engine by Leopold, A. D. 1720, the receivers were placedbelow the water they were to raise : hence the principle of condensationwas not required—for as soon as the steam expelled the contents of a re-ceiver, a communication was opened between the upper part of the latterand the atmosphere, so as to allow the steam to escape and a fresh supplyof water to enter below. He produced a rotary movement by dischargingthe water into the buckets of a water-wheel.
When steam is admitted into a receiver, a portion is immediately Con-densed by the low temperature of the vessel and the cold water within;so that not tili a film or thin Stratum of hot water is thus formed on thesurface, can the full force of the vapor be exerted in expelling the contents.This waste of steam is not however so great as might be imagined, becausethe water with which it comes in contact still remains on the surface,having become lighter than the mass below by the accession of heat, andconsequently preventing the heat from descending : yet various attemptswere made to interpose some non-conducting substance between the steamand the water. Papin, as we have seen, used a floating piston. In 1766,Mr. Blakey, an enterprising English mechanic, took out a patent for theapplication of a Stratum of oil or air. To use these he made some eorres-ponding alterations in the receiver; but the advantages were not so greatas had been expected. Blakey also introduced a new boiler, consistingof tubes or cylinders completely filled with water and imbedded in thefire. It caused considerable excitement among scientific men, but thedanger arising from them, and the explosion of one or more, caused themto be laid aside. He spent several years in France , where he erectedsome of his engines. He wrote on several subjects connected with thearts. There is a copious and interesting extract from his Dissertation onthe Invention and Progress of Fire Machinery, in the Gentlemen’s Maga-zine for 1792, page 502.
Other modifications of Savery’s engine were made previous to andabout Blakey’s time, of which no particular accounts are now extant. Inhis Comparisons of French and English Arts, (article Horölogy ) Blakeysays, “About 1748 another Swiss, named Rivatz , appeared in Paris :he understood all the known principles and methods for regulating time inequal parts, to which he added others of his invention..And I