8 Experiments on Wkinftone and Lava, 



would do bed for fmelting iron, where fome degree of darapnefs in the blaft is rather 

 beneficial. 



To defcribe the apparatus minutely for this purpofe, would fwell this paper to too great 

 a bulk ; but of it& poffibility I could eaGly convince any one, and would engage to conftru£b 

 it, in fuch a fituation as before mentioned, at an expence comparatively trifling to any 

 other mode of caufing a blaft, where a fall of water could not be procured. 



Even where fuel is not very cheap, yet fteat»\,may be applied to the purpofe of ventilation 

 with this inftrument, in the manner hinted at here, to great advantage, in thofe fituations 

 where labour is difficult to be procured, or inconvenient to be ufed ; or where habits and 

 prejudice operate ftrongly againft working manual ventilators. This laft is too frequently 

 the cafe aboard men of war, and other fliips, though in no other place is ventilation fo ne- 

 ceffary to preferve health, and fecure provifions from decay. 



An apparatus for ventilating fhips in this manner might eafily be fixed befide the fhip's 

 boiler, to be ufed in calms, when the wind would not operate on the inftrument before 

 defcribed, and which at other times might be applied to boil water for various ufes; and 

 the fliip's boiler itfelf might be fo adjufted as to ferve for this purpofe, without preventing 

 cr impeding its ufe in preparing provifions. 



To conclude, I will juft mention a matter this fubje£t has fuggefted of forae importance, 

 though fomewhat differing from what has already been treated of. 



From obferving the effects of the conical opening in the blaft ventilator, it occurs, that 

 walls might be fo conftrufted about a windmill, as to operate in a fimilar manner, and that 

 thus the wind might be conduced with increafed force, to operate in any direction required 

 ftn a fixed wind wheel, though it blew from various direftions; and that a windmill thus 

 Conftru(Sled, would have the additional advantage of being capable to be regulated or 

 flopped at pleafure, in a manner fomewhat fimilar to a water-milh' This mode of con- 

 ftrudting thofe mills would prevent many fatal accidents ; and would not coft fo much as 

 might at firft feem, as the granaries, and other buildings annexed to them, might be fo 

 arranged, as in a great meafure to anfwcr the purpofe of the walls propofed to be built *. 



III. 



Experiments on Whinjlone and Lava. By Sir James Hall^ Bart. F. R.S. Js* F, A. S, 



Edin f . 



T, 



HE experiments defcribed in this paper were fuggefted to me many years ago, when 

 employed in ftudying the geological fyftem of the late Dr. Hutton, by the following plaufible 

 objedtion, to which it feems liable. 



* On the fubjeft of this paper, fee Phil, Journ. I. II. Art. Venturi. N. 

 t Read before the Royal Society of Etdinburgh, and communicated by the author. An abridged ac- 

 count of the content* of this paper was given in our Journal II, 185. 



Granite, 



