172 THE ROYAL SOCIETY OF CANADA 
O, from coincidence with AB to coincidence with CD will be denoted 
by AB + CD; if the total rotation is less than a complete revolution, 
the angle will be denoted by (AB+CD). If OR turn clockwise on 
O from coincidence with CD to coincidence with AB, the angle so 
described will be denoted by CD— + AB, or by (CD— + AB) if the 
total rotation is less than a complete revolution. If A, C and O 
coincide, the angle (OB + OD) may be denoted by (4 BOD). 
4. The triangular figure formed by the three points A, B, C and 
the three lines AB, BC, CA, will be denoted by ABC or by abe, 
wherein a=BC, b=CA and c=AB. Also (ABC) will denote the 
triangle with perimeter (AB), (BC), (CA), the perimeter being de- 
scribed from A through B to C, thence along (CA) to A; and (ACB) 
will denote the same triangle but with perimeter described from A 
through C to B thence along (BA) to A. 
5. The tetrastigm (complete quadrangle) formed by four coplanar 
points A, B, C, D, their six connecting lines a=BC, b=CA, c=AB, 
a’=AD, b’=BD, c’=CD, and the Cevan points A’=aa’, B’=bhb’, 
C’=cc’ will be denoted by ABC; D. The tetragam (complete 
quadrilateral) formed by four coplanar lines a, b, ¢, d, their six inter- 
section points A= be, B=ca, C =ab, A” =ad, B” =bd, C”=cd, and the 
diagonal lines a” = AA”, b”=BB’, c’=CC’ will be denoted by abe; d. 
A”, B” and C” are the Menelaän points of abe; d. 
6. The numeric of a geometrical magnitude is the numerical 
measure of the magnitude affected with the positive or the negative 
sign as the case may require. Thus, if p denote the numerical measure 
of the length of the line-segment (1) terminated by the points A and 
B, and if +p) be chosen as the numecic of the directed segment (AB), 
—p will be the numeric of (BA). If 8 denote the numerical measure 
of the rotation of the radian OR from coincidence with OB to first 
coincidence with OD, and if +6 be selected as the numeric of 
(OB+OD), —é6 will be the numeric of (OD—+OB). If A denote 
the numerical measure of the area of the triangle with angular points 
A, B and C, and if +A be selected as the numeric of (ABC), then 
will—A be the numeric of (ACB). 
7. Symbols printed in italic type denote the numerics of the 
magnitudes of the geometrical figures denoted by the similar symbols 
in Clarendon type, parentheses that would be superfluous in the 
italics being omitted. Thus AB is the numeric of (AB), BA is the 
numeric of (BA); (AB £ CD) is the numeric of (AB4+CD), and ABC 
is the numeric of (ABC); but sinQOR means sin (“QOR) and simi- 
