ELASTIC FLUIDS. 283 



J caiinot however, on this occafion, avoid adverting to fome The remarkable 



experiments of Dr. Piieftiey, which few modern philofophers pSir^of^air 



can be unacquainted with : I mean ihofe relating to the Teem- entering earthen 



ing converfion of water into air. (Vid. Phiiof. Tranfadt. "'^'^^ ^^''« 



'z ^ water paffed out 



vol. 73, page 414, — or his Expls. abridged, vol.2, page in a vaper. 



407.) He found (hat unglazed earlhern retorts containing a 

 little moifiure, when heated, luiniilted the external air to pafs 

 through their pores at the fame time that aqueous vapour 

 paiTed through the pores the contrary way or outward ; and 

 that this lafi: circuniftance was necejfary to the air's entrance. 

 The retorts are air-light, fo far as that blowing into them 

 difcovers no pores ; but when fubjecled to a greater preflure, 

 as that of the atmofphere, or even one much fliort of it, they 

 are not able to prevent the paflage of elaftic fluids. The fadl 

 of air paffing into the retort through its pores, and vapour 

 out of them at the fame time, are elegantly and moft con- 

 vincingly (hewn by Dr. Prieftley's experiments, in which 

 he ufed the apparatus reprefented in plate 7, fig. 1, of the 

 edition above referred to. The Dodor confeifes his explana- 

 tion of thefe remarkable fads is very inadequate; and no 

 wonder, for it is impoflible for him or any other to explain 

 them on the commonly received principles of elaflic fluids. 

 But we will hear what he fays on the lubjed :—" At prefent Dr.Prleftley's 

 it is my opinion, that the agent in this cafe is that principle cynu^ures." 

 which we call aUraRlon of co/tejion, or that power by which 

 water is raifed in capillary tubes. But in what manner it 

 acls in this cafe I am far from being able to explain. Much 

 lefs can I imagine how air (hould pals one way and vapour 

 the other, in the fame pores, and how the tranfmiffion of the 

 one fliould be necefTary to the tranfmiffion of the other.— 

 1 am fatisfied, however, that it is by means of fuch pores as 

 air may be forced through, that this curious procefs is per- 

 formed ; becaufe the experiment never fucceeds but in fuch 

 vefTels as, by the air-pump at leafl, appear to be porous, 

 though in all fuch.^' 



The truth is, thefe fads fo difncult to explain are exaaiy The faft is, that 

 fimilar to thofe which are the fubjecl of this memoir ; only in- ^j^ ^j^^ {,„ 

 fiead of a great numhtr of pores we have one of fenfible mag. means of the 

 nitude, (the bore of the tube.) Let the porous retort have f°"** 

 the fame eiaflic fluid within and without, in the one cafe; 

 and the two phials contain the fame elaftic fluid in the other, 



then 



