The Perspectograph.
This simple instrument, invented by Mr. Jarlot, renders the tracing of a sketch extremely easy, besides avoiding absolutely faults of perspective, which is, without doubt, the principal advantage of this instrument. Thanks to it, one obtains an easy reproduction on one plane of objects placed on different planes.
Here is a description of this very simple instrument. A wooden frame A B C D, with a slot in the side, A B, in which a pane of glass can slide so as to cover the whole space of the frame, a, b, c, d, is fixed on a stand.
The frame is maintained in a perfectly horizontal position by means of a water level n n’, placed on the lower side of the frame. At E is a small rule moving on a hinge at E, allowing the angle to be varied at the plane A B C D, by resting it on two supports E E’.
The supports themselves move round on an axle fixed on the rule. At the extremity E’ of this rule is fixed a copper blade curved in E’, C’, and pierced by a small hole of about an eighth of an inch in circumference, the edges are made thinner as represented in the diagram placed above; the widened part is turned toward the frame.
So much for the body of the instrument, now for the accessories. In the slot left in side, A B C D, lower a glass pane covering the space, a, b, c, d, which is not, however, a necessary condition, it depends on the size of the design you desire to take.
This pane requires a little preparation. It is done in this way: One chooses a pane of the desired glass, as free as possible from defects. Cover one side only with turpentine, and which you know is a natural varnish.
See that this coating is as thin as possible, and to ensure this, go over the surface with a very soft brush steeped in the liquid. When you see that the latter does not run any more, leave off brushing. Let it dry for two days if necessary; take care, meanwhile, to protect the varnished side from dust.