PPT Slide
The columns in each order ought to be form’d in ?uch a manner, that the diameter of the upper part of the column may be ?maller than at the bottom, with a kind of a ?welling n the middle.
As to the manner of making the ?welling in the middle, we have no more to ?hew from VITRUVIUS but his bare promi?e; which is the rea?on that mo?t writers differ from one another upon that ?ubject.
The method I u?e in making the profile of the ?wellings is this; I divide the fu?t of the column into three parts, and leave the lower part perpendicular; to the ?ide of the extremity of which I apply the edge of a thin rule, of the ?ame length, or a little longer than the column, and bend that part which reaches from the third part upwards, until the end touches the point of the diminution of the upper part of the column under the collarino. I then mark as the curve directs, which gives the column a kind of ?welling in the middle, and makes it project very gracefully.
And although I never could imagine a more expeditious and ?ucce?sful method than this, I am neverthele?s confirmed in my opinion, ?ince Signor PIETRO CATANEO was ?o well plea?ed when I told him of it, that he gave it a place in his Treati?e of Architecture, with which he has not a little illu?trated this profe??ion.
A B, the third part of the column, which is left directly perpendicular.
B C, the two thirds that are dimini?hed.
C, the point of diminution under the collarino.
Procedure for defining the entasis of a column