H) Mr Levy on the modes of Notation 
to EF, the number of rows in breadth is greater than the num- 
ber in height ; and the contrary takes place when it is parallel 
to EL. The sign by which such rhomboids are represented, is 
a**, n being greater than 1 in the first case, and less in the se- 
cond ; and ’ 
AD:AF::w:l; or AD : AL : : w : 1. 
When one of the faces of the secondary rhomboid is parallel 
either to EM or EN, it is said to be produced by a decrement 
in height or breadth, on the inferior angle of the rhomboid, and 
the sign corresponding is where n is less than 2, in the first 
case, and greater in the latter, and where the following propor- 
tions respectively obtain : 
CB:CM::w:l, CB:CN::7i:l. 
The formulge relative to the two last cases may, however, be 
deduced from those relative to the two first, by considering n as 
negative, as it will be evident if we produce EM, EN, till they 
meet AD on the other side of A. 
It is therefore sufficient to consider the firs : of these four cases. 
From E draw EG perpendicular upon AB, this line produced 
will pass through D ; from F draw FK perpendicular upon AB ; 
we shall have successively 
(n — 1) AG 
ATT 
AK = 9 
n 
KG 
n 
n 11 
KH 
2HG _ (n-f-2)HG. 
: 9 Ivtjr — ’ 
therefon 
n 
2) HG . 
n 
or 
AG : HG 
1 ; 
{n — 1) AG 
n 
but 
AG : HG : : tan AEG : tan HEG : : tan EHG : tan EAG ; 
therefore, 
tan EHG : tan EAG : : -f S : n — ■ 1 ; or, which is the same 
thing, 
tan ((a”, a’) — 90'’) : tan ((P, a!) — 90°) : -f 2 : n — l...(A). 
n -j” S ’ ’ 
This proportion will give the value of — -y, and consequent- 
ly that of when the incidence of one of the faces of the sccon- 
