Chap. 8.] Leopold’s Engines. 331
canal n’empöchent point l’eau d’agir avec violence, et la force avec la-quelle eile agit est d’autant plus grande, que les hommes qui font aller lapompe, emploient eux-mbmes plus de force, la quantite d’eau depend en-core du nombre de pistons.”
In 1699 Perier obtained from the king an exclusive privilege to con-struct fire-engines, which Professor Beckman thinks were the first publicones employed in Paris . In 1716 an ordinance of tbe king directed alarger number than those already in use, to be distributed in differentparts of the city, and public notice to be given where they could be foundin case of fire. a In 1722 there were thirty in use, besides others belong-ing to public buildings. As these machines had air vessels, it is strängethat Belidor neither mentions the fact nor refers to Paris engines at all.After describing a Dutch one, No. 148, he quotes (as if he knew of no otherswith air vessels) Perrault’s description of the one that was in the king’slibrary fifty years before, and an account of another that Du Fay saw atStrasbourg in 1725.
Leopold’s engines do not appear to have possessed any peculiar featureto which he could lay claim as inventor. They seem to have been iden-tical or nearly so with the one described in the Journal des Savans fbrtyyears before, (No, 147.) Each consisted of a single pump with an air ves-sel enclosed in a copper ehest. One man raised a jet by it to the heightof from twenty to thirty feet. Leopold kept the construction for sometime a secret, and with this view the pump was entirely enclosed in theehest; a cover being soldered on the latter. Beckman says he made andsold a great number of them. In 1720 he published a description of themin a pamphlet; and in 1724 he inserted an account of them in bis TheatrumMachinarum Hydraulicarum, a work published that year at Leipsic inthree volumes folio.
The annexed figure, No. 148, exhibits an improvement on Leopold’s
engine, having two cylinders andworkingby a double lever. Smallengines seem to have been prefer-red to those of large dimensions,such as were made by Hautsch,or those of modern times. Beforethe introduction of hose pipes,small ones were certainly moreuseful, since they could be carriedinto any part of a house when onfire, but when flexible pipes of lea-ther and canvas became common,their efficiency was not to be com-pared with that of the large sizes.
English fire-engines were much the same dimensions as those usedon the continent tili Newsham and Contemporary engineers introducedothers that approached in size those in present use ; but for severalyears after the smaller ones retained the preference. The London ma-nufacturers made six different sizes, the larger one only being placedon wheels. Even in the middle of the 18th Century such as are re-presented by the figure on the next page were common in that city. Asimilar figure was published by Mr. Cläre in 1735 in his work on themotion offluids, and so late as 1765 it was described (in the London Ma-gazine for that year) as the engine in common use. As an indication that