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The diameter of the circular light at top is 27 feet 
5 inches, equal to 29209,7 ; which, divided by 30, 
gives 5>73 t for the Roman foot. Whether Defgodetz 
took more meafures than one of this diameter, does 
not appear, nor how he took it. It is probable, that 
30 Roman feet was the meafure here intended, being 
a round number, and one fifth of the diameter be- 
tween the centers of the columns : but the making 
this light a tiue circle, precifely anfwering to. a 
given meafure, was a difficult piece of workmanfhip. 
Therefore, this meafure is of lmal 1 authority. 
The fquare compartments on the pavement mea- 
fure 9 feet of inch, or 9647,79 London parts; 
which, divided by 10, give a foot of 964,8 parts. 
But Defgodetz obferves (9), that this is not the ori- 
ginal pavement : and this meafure of the foot anfwers 
to the age of S. Severus, as I fhall fhew hereafter. 
This pavement being confiderably raifed above the 
old one, no meafures of uprights taken from it are 
of any authority. 
The height of the attic, above the cornice it ftands 
upon, i$ 27 feet 2f inches, equal to 29010 ; which, 
divided by 30, gives a foot of 967 parts. But the 
walls of this building being brick, this meafure may 
have been diminifhed by their fettling, as the whole 
error occafioned by it might be made to fall on this 
part, rather than on the order below. 
The length of the fhafts of the columns in the cir- 
cular range, is 27 feet if inches, == 28884,18; 
which anfwers to 29^ feet, of 970,9 parts each. 
(9) Defgodetz, p. 41. 
The 
