126 REPORT—1840. 
to the presence of water, there being at all times the samme quantity of 
alkali present in the fuel, whatever that might have amounted to, pro- 
ducing no such effect, the experiment seems to establish, at very high 
temperatures, a powerful action of water on siliceous matter. To attri- 
bute the action to alkali would not lessen the difficulty, both because 
under perfectly similar circumstances, when there was no water, no 
effect was produced, and because each pound of alkali would have had 
to dissolve, perhaps, forty pounds of silica. Mr. Jeffreys was informed 
by a military engineer of distinguished ability, to whom he related the 
experiment, that he had once observed a similar destructive effect upon 
the brick casing of a kiln, by moisture getting in at an intense heat, 
though no scientific notice was taken of it at the time; and as coal 
was the fuel in this case, there was still less ground for supposing the 
action to be alkaline. Lastly, if alkali did play an appreciable part, 
the experiment would remain still sufficiently curious, as it showed an 
abundant vapourization of silica, by a fraction of its weight of alkali, 
without the aid of fluorine, a phenomenon which has, so far as the 
author is aware, been only obscurely manifested in minute quantities, 
as noticed by the late Dr. Macculloch.* 
An Account of the Construction of the Models of the Island of Achil, 
Clare Island, and the South-Western district of Mayo, in Ireland. 
By Wii Batp, F.R.S.E., M.R.LA,, Se. 
“ The chief object of this paper is to call attention to the cultivation 
of an art hitherto but little practised in Great Britain or Ireland, in 
representing the irregularities of surface, i.e. the rise and fall of 
ground in a country by modelling, and also to give an account of some 
models which I have constructed of parts of the West of Ireland, 
since 1815. 
The first work of this kind I made, was a model of Achil, the largest 
island on the coast of Ireland; it contains fifty-eight English square 
miles of lofty ground, and has been deposited in the museum of the 
College of Edinburgh. The second model made was that of the 
Barony of Murrisk, containing nearly two hundred square miles, and 
which occupied me at intervals for a period of nearly five years; it 
was formed of putty, white-lead and cork. 
J also constructed a model of Clare Island, on the west coast of Ire- 
land, an island which is four English miles long, by two and a quarter 
in its greatest breadth. A cast of this model was deposited, on the 
26th of April, 1830, in the French National Institute, and another one 
in the model department of the Bibliothéque du Roi, at Paris, and 
were on ascale of eight inches to the Irish mile; but the models of 
Achil Island and Murrisk Barony were on scales of four inches to the 
* Professor Johnston and Mr. Jeffreys have been requested to prosecute re- 
searches on this subject. 
| ian. apes 
