Description of the Camera Lucida. 347 



its principal focus. The stem of the instrument (which 

 sUdes) is accordingly marked at certain distances, to which 

 the conjugate foci are in the several proportions of two, 

 three, four, &c. to one; so that distinct vision may be ob- 

 tained in all cases by placing the painting proporlionally 

 ujore distant. 



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

 ment, and reversing the proportional distances, the artist 

 might also enlarge his smaller sketches in any proportion 

 with every desirable degree of correctness ; and the natu- 

 ralist, bv employing a deeper lens, might delineate minute 

 objects in any degree magnitied. 



Since the primary intention of the camera lucida is al- 

 ready, in some measure, answered by the camera obsczira, a 

 comparison will naturally be made between them. The ob- 

 jections to the camera obscura are, 



1st, That it is too large to be carried about wiih conve- 

 nience; but the camera lucida is as small and portable as 

 can be wished. 



2d, In the former, all objects that are not situated near 

 the centre of view are more or less distorted. 



In this there is no distortion ; so that every line, even the 

 most remote from the centre of view, is as straight as those 

 that pass through the centre. 



3dlv, In that the field of vievv does not extend more than 

 30, or at most 35 degrees, with distinctness. 



But in the camera lucida as much as 70 or SO degrees 

 might be included in one view. 



As it has been tliouglit advisable to secure an exclusive 

 sale by patent, those who are desirous of purchasing the in- 

 strunjcnt are informed that Mr. Newman, No. 24, Soho- 

 fe^uare, has at present the disposal of it. 



LIX. On 



