CAMEtlA LUCIDi. 



DBtrtictions. 



It answers 

 every purpose 

 of the penta- 

 graph. 



Method of 

 using the in- 

 -Mrument for 

 this purpose. 



Magnified de- 

 signs. 



strument is to facilitate the delineation of objects in trn't? 

 perspective, yet this is by no means the sole purpose to 

 which it is adapted ; for the same arrangement of reflectors 

 may be employed with equal advantage for copying what 

 has been already drawn, and may thus assist a learner in 

 acquiring at least a correct outline of any subject. 



For this purpose the drawing to be copied should be 

 placed as nearly as may be at the same distance before the 

 instrument that the paper is beneath the eye-hole, for in 

 that case the size will be the same, and no lens will be ne- 

 cessary either to the object, or to the pencil. 



By a proper use of the same instrument, every purpose 

 of the pentagraph may also be answered, as a painting may 

 be reduced in any proportion required, by placing it at a 

 distance in due proportion greater than that of the paper 

 from the instrument. In this case a lens becomes requisite 

 for enabling the eye to see at two unequal distances with 

 equal distinctness, and in order that one lens may suit for 

 all these purposes, there is an advantage in carrying the 

 height of the stand according to the proportion in which 

 the reduction is to be effected. 



The principles on which the height of the stem is adjusted 

 will be readily understood by those who are accustomed to 

 optical considerations. For as in taking a perspective 

 view the rays from the paper are rendered parallel, by 

 placing a lens at the distance of its principal focus from the 

 paper, because the rays received from the distant object* 

 are parallel ; so also when the object seen by reflection is 

 at so short a distance that the rays received from it are in a 

 certain degree divergent, the rays from the paper should be 

 made to have the same degree of divergency in order that 

 the paper may be seen distinctly by the same eye ; and for 

 this purpose the lens must be placed at a distance less than 

 its principal focus. The stem of the instrument is ac- 

 cordingly marked at certain distances to which the con- 

 jugate foci arc in the several proportions of 2, 3, 4, &c. 

 to 1, so that distinct vision may be obtained in all cases, by 

 placing the painting proportionally more distant. 



By transposing the convex lens to the front of the in- 

 strument and reversing the proportional distances, the artist 

 might also enlarge his smaller sketches with every desirable 



degree 



