68 Description of the Optigraph. 



Fig. 1. (Plate II,) is a perspective view of the-optigraph, 

 A represents the drawing board, on the outside frame of 

 which is fixed the pillar of the instrument, B, by a clamp a. 

 C is a tube (sliding, in the pillar), on the top of which is 

 fixed, by means of a screw c, the frame D ; at the end of 

 this frame is a plain mirror E, beneath which is suspended, 

 by a universal joint, the telescope F, of which G is the eye- 

 tube. H are sliding tubes, capable of being shortened or 

 lengthened in the same propoiuon as the inside speculum c, 

 (fig. 2) which is fixed to any place by tiie clamp screw E. 

 The pencil l,, of which k is the handle, slides perfectly easy, 

 without shake, in the tubes H : the pencil is so contrived as 

 to have all the freedom of a pen when held in the hand for 

 use. 



Fig. 2. represents a section of the telescope, being the 

 principal part of the invention. The rays from an object 

 entering the plane mirror a, are reflected mto the telescope, 

 passing through the object-glass b, and entering the speciduni 

 c, are reflected through the eye-glass d, to thu eve at e: fh 

 a piece of parallel glass, with a small dot on ita centre, ex- 

 actly in the focus of the eye-glass d. 



Mode of using the Optigraph. 



Fix the drawing board to the table (by a clamp which is 

 packed in the box) so that the surface of the mirror E is 

 nearly parallel to the object ; then take hold of the handle h, 

 "and hold the pencil on that part of the paper where you 

 would wish the centre of your drawing, or any part thereof, 

 to be. Then place your eye at the eve- tube G, and with 

 your left hand alter the inclination of the mirror E until the 

 small dot, described at /, in fig. 2., is on some particular 

 part of the object that you wish to begin with, adjusting the 

 telescope to distinct vision by the milled head P. Then 

 by moving your hand (having the pencil) you pass the dot 

 seen in the field of the telescope over the object, the pencil 

 marking it at the same time on the paper. 



To make your drawing larger, pull out the tube of the 

 pillar C, fig. 1, and fix it with the screw e ; then pull out 



the 



