Upon each of the four Corners of this _Coffin_ is let in and fastned down a square Iron Plate as at _a a a a_, with Return Sides about six Inches long each side, half a quarter of an Inch thick, and two Inches and a quarter broad; upon the upper outer-sides of each of these Plates is fastned down to them with two or three Rivets through each side, another strong Iron half an Inch deep, and whose outer Angles only are square, but the Inner-Angles are obtuse, as being sloped away from the Inner-Angle towards the farther end of each inner-side, so as the _Quoins_ may do the Office of a Wedge between each inner-side and the _Chase_. [Illustration: _Plate 7._] The Plates of these Corners (as I said) are let in on the outer Angles of the upper-side of the Frame of the _Coffin_, so as the upper-sides of the Plates lye even with it, and are Nailed down, or indeed rather Rivetted down through the bottom and top-sides of the Frame of the _Coffin_, because then the upper-sides of the Holes in the Iron Plates being square Bored (that is, made wider on the upper-side of the Plate, as I shall shew when I come to the making of _Mathematical Instruments_) the ends of the Shanks of the Iron Pins may be so battered into the Square-boring, that the whole Superficies of the Plate when thus Rivetted shall be smooth, which else with the exturberancies of Nail-heads would hinder the free sliding of the _Quoins_. At the hinder end of the Frame of the _Coffin_ are fastned either with strong Nails, Rivets, or rather Screws, two Iron _Half-Joynts_, as at _b b_, which having an Iron Pin of almost half an Inch over put through them, and two _Match-half-Joynts_ fastned on the Frame of the _Tympan_, these two _Match-half-Joynts_ moving upon the Iron Pin aforesaid, as on an _Axis_, keeps the _Tinpan_ so truly gaged, that it always falls down upon the _Form_ in the place, and so keeps _Register_ good, as shall further be shewed in proper place. Behind the _Coffin_ is Nailed on to its outside, a Quarter, as at _c c_ this Quarter is about three Inches longer than the breadth of the _Coffin_, it hath all its sides two Inches over, and three of them square; but its upper-side is hollowed round to a Groove or Gutter an Inch and an half over. This Gutter is so Nailed on, that its hither end standing about an Inch higher than its further end, the Water that descends from the _Tympan_ falling into it is carried away on the farther side the _Coffin_ by the declivity of the farther end of the Gutter, and so keeps the Planck of the _Carriage_ neat and cleanly, and preserves it from rotting.