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XXIV . Pbe principal Properties of the Engine for turning 
Ovals in Wood or Metal , and of the Injlrument for 
drawing Ovals upon Paper, demonjlrafed. By the Rev . 
Mr. Ludlam, Vicar of Norton, near Leicefter; com- 
, 
municated by the Aftronomer Royal. 
Read May 4, 1780. 
r I ^ H E inftrument for drawing ovals upon paper or 
board is fo common, that a particular defcriptioii 
of it is needlefs. It is much in ufe among the joiners, 
and called by them the trammels. One part of it con lifts 
of a crofs with two grooves at right angles : the other is 
a beam carrying two pins which Hide in thofe grooves, 
and alfo the defcribing pencil ; we fhall diftinguilh thefe 
two parts by the names of the crofs and the beam. 
It is very well known, that all the engines for turning 
ovals are conftrudted on the fame principles with the 
trammels; the only difference is, that in the trammels 
the board is at reft, and the pencil moves upon it ; in the 
turning engine, the tool (which fupplies the place of the 
pencil) is at reft, and the board moves againfl: it. 
Let 
