Note 46 — LETTERS AND PAPERS ON PHILOSOPHICAL SUBJECTS. (continued 5)
Reading edition
The shutter is slid up and down in this manner, only in those fire-places which are so made as that the distance between the top of the arched opening, and the bottom plate, is the same as the distance between it and the top plate. Where the arch is higher, as it is in the draught annexed (which is agreeable to the last improvements) the shutter is set by, and applied occasionally; because if it were made deep enough to close the whole opening when slid down, it would hide part of it when up.