Perspective Draiving . £55 
After having multiplied and varied his experiments in 
such a manner as to present positive results, M. Lepere, 
in conjunction with the committee of engineers appointed 
to examine his experiments, draws the following conclu- 
sions : 
1st. That the schist of Cherbourg, when strongly cal- 
cined and pulverised, forms an excellent mortar when 
mixed with sour lime. 
Sdly. That in order to give precisely the same proper- 
ties to schist which are possessed hy puzzolana and ter- 
rass, the former must be calcined in a reverberating, in- 
stead of a lime, furnace. 
No. 50. 
Description of a very simple and useful Scale , for di~ 
viding the vanishing Lines in Perspective . In a 
Letter from 6 , Cumberland, Esquire , to Mr . Ni- 
cholson.* 
(With an engraving.) 
SIR— Having been in the habit of drawing for my 
amusement all my life, and feeling the value of that ac 
quirement, it has been my practice to recommend to 
others as much of that acquisition as can with very little 
trouble be attained ; I mean the putting into perspective 
common objects ; such as simple landscapes, machines, 
buildings, and the interior of apartments, manufactories, 
&c. And where I have had an opportunity to give four 
or five close lessons, I have generally seen my end ob- 
tained to their great satisfaction, without ever showing 
them the Jesuits , or any other voluminous treatise; books 
that have hindered more the study of art, than they have 
ever made artists ; for a moment’s consideration on this 
* Nicholson, vol. 16, p, L 
