Part IV. Of Things relating to Matbematkfyj&c. 363 
pieces, without any other Prop than on the fides, for 
Vines, or other like Plants to run upon, fo as to (hade the 
whole. 
Note here, That whereas the ends of the feveral pieces 
are to lie upon thofe that crofs them, about the middle 
thereof 3 it will be neceuary at every Joynt to abate both 
pieces half way, or near it 3 that one may be thus let into 
the other, and the whole reduced to a Flat. But whether 
fuch piece, fo abated doth end even with that on which it 
lies, or doth lie over fomewhat beyond it 3 is indifferent. 
And though That may (eem more elegant 3 This, perhaps, 
may be fitter for ufe. 
Each piece, I fay, muft be fo abated half way, or near 
it. For, whereas thofe Beams, efpecially if of a confidera- 
ble length, will, with the weight, bow a little 3 if this abate- 
ment be fomewhat lefs than half way, ( whereby without 
fuch bowing, the whole would fomewhat rife in the mid- 
dle ) it will by fuch bowing be reduced to a Flat. 
Notealfo, That a Frame thus contriv'd, needs neither 
Nail nor Pin 3 the feveral pieces faftening,as well asfupport- 
ing one another. Yet,if it be to bear a great weight more than 
its own 3 it will be convenient to faften each Joynt with 
Pins 5 and, if need be, to ftrengthen it with Iron-Plates, or 
line it with other pieces of Timber, to be faften'd with Iron- 
Bolts 5 to make amends for what is weaken d by the abate- 
ments at the Joynt s : which will make the whole Frame 
exceeding ftrong. 
A Model of a Double Winding STAIR-CASE. The 
Foot of one is oppolite to that of the other 3 whereby 
both make a parallel afcent, and within the fame Cylinder. 
The Newel or Column in the Centre, is hollow, and built 
with long Apertures, to convey Light, from Candles placed 
at the bottom, and on the fides of the Newel, into both 
the Cafes. 
Another, of a fingle one, with a folid Column or Newel. 
Navigation. A Model of the Hull of a DOUBLE-BOT- 
TOM'D SHIP. Contrived by Sir William Pettey. 
It hath two Heads, two Ruder s, two Keels, two Holds, 
and a Vacancy between them. 
From Stem to Stern, four feet and feven inches long. 
The Deck.-> about four Feet. From the foremoft Rib to 
Aaa 2 the 
