Mr. Weaver on Irish Tin Ore. 27 



generated, because running down the pressure always di- 

 minishes the electricity in a much greater degree than is due 

 to the mere decrease of density, and frequently changes the 

 electricity of the jet from positive to negative, I find the most 

 convenient way of using my apparatus is to place it out of 

 doors, and to convey the electricity into the house by means 

 of a wire. If, however, the steam were discharged horizon- 

 tally it might be projected into a chimney, or out of a window, 

 and the objection to using the apparatus within doors would 

 be in a great measure removed. 



Dr. Ure, who has witnessed a repetition of most of the 

 experiments I have described, suggested a method of reple- 

 nishing the boiler without exhausting the steam. He proposed 

 to attach to the boiler a cylindrical vessel, of convenient dimen- 

 sions, having a stop-cock at the top to receive the water, and 

 another at the bottom to communicate with the boiler. By 

 closing the upper cock, after filling the vessel with water, and 

 then opening the lower one, the water would pass into the 

 boiler without permitting any escape of steam to take place. 

 This arrangement I would certainly recommend to any one 

 who may feel inclined to construct an electro-steam apparatus. 



The production of electricity by steam has several important 

 advantages over the common method of obtaining it. An 

 electro-steam apparatus is self-acting, which leaves the ope- 

 rator at perfect liberty to attend to results. Its high tempera- 

 ture renders its action independent of dampness in the atmo- 

 sphere, which so greatly impairs the energy of an electrifying 

 machine; and finally, its extreme simplicity secures it from 

 injury or derangement. 



Wm, Geo. Armstrong. 



Newcastle-upon-Tyne, 9th May, 1841. 



IV. On Irish Tin Ore. By Thomas Weaver, Esq., F.R.S., 

 F.G.S., M.R.I.A., $c. S?c* 



IN a paper drawn up by Aquila Smith, Esq., M.D., on Irish 

 Tin Ore, read before the Geological Society of Dublin, on 

 the 9th Dec. 1840, and published in the London, Edinburgh 

 and Dublin Philosophical Magazine and Journal of Science 

 for February 1841, it is stated, "The question has been often 

 asked, is tin ore found in Ireland ? and I believe the only re- 

 ply which could be given is, that it was said to have been found 

 in the county of Wicklow, about the year 1796, when the gold 

 mines were worked on account of the Government." 



It is also stated, that the existence of tin ore in Ireland was 

 announced for the Jirst time in the report of Messrs. Mills, 



* Communicated by the Author. 



