On some Effects produced by a Fluid in Motion. 209 



M. Lamarle, and which, by an ingenious way of treating them, 

 he is able to refer all to the same principle are exactly those 

 which lead to the real results obtained — to those, that is, given 

 by the experiments with the skeletons of iron wire. 



To sum up, M. Lamarle has solved questions which seemed 

 extremely difficult, and his investigation is an important contri- 

 bution towards a complete theory of liquid films. 



XXV. On some Effects produced by a Fluid in Motion. 

 By George F. Rod well, F.C.S.* 



[With a Plate.] 

 No. II. On the Trompe. 



A STREAM of water falling through a tube may, under c er ~ 

 tain conditions, be caused to carry down air with it, which 

 air, when removed from the direct influence of the stream, is able 

 in virtue of its small specific gravity compared with water, to sepa- 

 rate itself therefrom, and maybe collected and employed for any of 

 the purposes for which a blast of air is requisite. An arrange- 

 ment for producing a blast by the above means has been in use 

 for the last 200 years, and is known as a trompe. 



I. 



Baptista Porta is said to have invented a machine for pro- 

 ducing wind by the flow of water ; but among the numerous 

 hydraulic machines which he figures in his work, entitled ' I tre 

 Libri de J Spiritali' (1606), I am unable to find one which bears 

 the least resemblance to a trompe ; neither, so far as I am aware, 

 is the trompe mentioned in the ' Mechanica Hydraulico-Pneuma- 

 tica' of Gaspar Schottus, nor in the ' Mundus Subterraneus ' of 

 Athanasius Kircher, although the latter was well acquainted with 

 the discovery. 



Grignonf states that the trompe was discovered in Italy about 

 the year 1640, but he gives no authority for the assertion. The 

 earliest account of the invention which 1 have been able to find 

 is in a work by Father Jean Francois, published in 1655 J, in 

 which there is a section entitled " Du Meslange des Eaux avec 

 l'Air, et d'une invention pour exciter un vent impetueux." In 

 this section Francois states that it had been recently discovered 

 that water is capable not only of dragging along with it terres- 

 trial bodies, but also air ; and that an arrangement for supply- 



* Communicated by the Author. 



+ Memoires de Physique sur I'art de fabriquer le fer, tiTen fondre et 

 forger des canons d'artillerie, &c. Paris, 1775. 



X Les Sciences des Eaux, qui explique en quatre parties leur formation, 

 communication, mouvemens, et meslanges. 



