250 PHILOSOPHICAL TRANSACTIONS. [anNO 1751. 



though nothing had been done at it from the time preceding ; which after a great 

 many trials made with this view, he also attributes to the moisture of the air 

 mixing with the oil. 



Mr. S. also endeavoured to render the pneumatic apparatus more simple and 

 commodious, by making this air-pump act as a condensing engine at pleasure, 

 by singly turning a cock. This not only enables us to try any experiments 

 under different circumstances of pressure, without changing the apparatus, but 

 renders the pump a universal engine, for showing any effect that arises from an 

 alteration in the density or spring of the air. Thus, with a little addition of 

 apparatus, it shows the experiments of the air-fountain, wind-gun, &c. 



This is done in the following manner : the air above the piston being forcibly 

 driven out of the barrel at each stroke, and having no where to escape, but by 

 the valve at the top ; if this valve be connected with the receiver, by means of 

 a pipe, and at the same time the ^alve at the bottom, instead of communicating 

 with the receiver, be made to communicate with the external air, the pump will 

 then perform as a condenser. 



The mechanism is thus ordered. There is a cock with 3 pipes placed round 

 it, at equal distances. The key is so pierced, that any 2 may be made to com- 

 municate, while the other is left open to the external air. One of these pipes 

 goes to the valve at the bottom of the barrel ; another goes to the valve at the 

 top, and a third goes to the receiver. Thus, when the pipe from the receiver, 

 and that from the bottom of the barrel, are united, the pump exhausts : but 

 turn the cock round, till the pipe from the receiver, and that from the top of the 

 barrel, communicate, and it then condenses. The third pipe in one case dis- 

 charges the air, taken from the receiver into the barrel ; and in the other lets it 

 into the barrel, that it may be forced into the receiver. 



LXX. Of /Jphyllon and Dentaria Hepiaphyllos of Clmius, omitted by Mr. Ray. 

 By Mr. fVilliam Watson, F. K. S. p. 428. 



Mr. Watson presented to the Society some specimens of 2 plants, then in 

 flower, which he said were not frequently found in England. One of them was 

 the anblatum of Cordus, or aphyllon of John Bauhin. This plant is deno- 

 minated squamaria by Rivinus, and dentaria crocodylia by Tabernaemontanus. 

 Linneus, in the Flora Suecica, calls it lathraea caule simplicissimo, corollis nu- 

 tantibus, labio inferiore trifido. Mr. Ray, in his Synopsis Plantarum Anglias, 

 takes notice of its being found near Dorking in Surrey, but the plant now pre- 

 sented was collected near Harefield in Middlesex, 



The other plant offered was the dentaria heptaphyllos baccifera of Caspar 

 Bauhin, or dentaria tertia baccifera of Clusius. This plant is treated of by Lin- 

 neus, in the Hortus Cliffbrtianus, and by Van Royen, in the Florae LeydensiS 



