TRANSACTIONS OF THE SECTIONS. 127 
English mile. The perpendicular scales, or those of height and depth, 
were the same as the horizontal.” 
The author thus describes his method of modelling : “1 drew out upon 
the smooth surface of a prepared board, made of deal-timber, an 
exact outline of the coast, lakes, rivers, roads, &c., &c., of the district 
to be modelled; and the different heights taken by the level, theodolite, 
sextant, and barometer, were correctly marked upon the board in their 
exact positions, by driving down small iron pins, the summits of which 
indicate the elevations, measuring the heights from the surface of the 
board as the level of the sea, at ordinary high water spring-tides; and 
all the spaces between the respective heights marked out by the iron 
wires were filled up with the putty ; but where the elevations were 
considerable, cork, cut into thin pieces, was used in combination with 
it, so as to give firmness, and prevent sinking, which would have been 
the case if large quantities of putty were used without adopting this 
precaution. 
The lakes are represented by different pieces of painted glass, the 
outlines of which were first traced upon the painted sides, which ap- 
peared like a fine hair line through them when laid in their positions, 
and the putty was wrought forward over the edges of the glass to the 
outlines of the lakes so traced out, but it was always necessary to keep 
the putty from touching any part of the painted glass underneath, for 
if it did the oil of the putty soon disfigured the water colour of the 
lakes. 
The model of Murrisk, containing, as before mentioned, nearly two 
hundred square miles, was formed of putty and white-lead ; the poison- 
ous qualities of which nearly destroyed my health, and I mention this 
circumstance as a caution to those who may hereafter be engaged in 
similar works. 
I found it extremely difficult to model in putty; and again much 
more so when combined with white-lead. What I found best and 
most easy to work with was pipe-clay, but then, when it dried, it 
always split into pieces. The best substance to construct or form 
models with is large blocks of chalk, closely joined together, and then 
to carve out the various forms of hill and vale; and when finished, to 
shade the surface over several times with prepared linseed-oil, by 
which means it will become highly indurated. 
The composition used by General Pfeffer for modelling was a mix- 
ture of charcoal, lime, clay, a little pitch, and a thin coat of wax.” 
To the communication from which the above extracts are taken, Mr 
Bald appended a notice of the rise of Topographic Maps. 
