258 Description of a Perspective Instrument . 
merit of this plain branch of the art; that, if you approve 
the idea, I shall with pleasure transfer from my portfolio : 
but with respect to the application of this already de- 
scribed, it will be necessary to premise, that the scale 
should be longer than the drawing-book each w ay ; by 
which means, by barely sliding it to the right or left, 
you can at pleasure place your point of sight more or less 
to the right, or left, or middle of the horizon; and, to be 
prepared for all circumstances, it would be as well to be 
provided also with a scale having a high horizon, and 
another with a very low one, such as the Dutch painters 
generally used, and which ever produces a picturesque 
effect, by giving many profiles of the elevations, and mul- 
tiplying the lines of light. 
Thus you have an easy expedient for a first help- 
practice will accomplish the rest; for we all know, or 
should know'’, that daily practice discloses to the indus- 
trious draftsman all the arcana of optical, aereal, and 
linear perspective, destitute, it is true, of terms to de- 
scribe his acquirement ; but to his own mind a perfectly 
intelligible and useful rule, by the help of which he can, 
w ith certainty, imitate all he sees on the theatre of the 
universe. I am, &c. 
George Cumberland, 
Bristol , December % 1806. 
NO. 51. 
Description of a Cheap , Simple , and Portable Instru- 
ment, for determining the Positions of Objects in tak- 
ing a Picture from the Life . By R. L. Edgeworth. 
Esquire 
(With an engraving.) 
THAT active and intelligent philosopher and jour- 
nalist, citizen Pictet, author of the Bibliotheque Brit- 
* Nicholson, rol. 1, p. 281. 
