From: A Course for Guitar-Flageolet, with Remarks on Guitar-Building. Vienna: Diabelli, 1832
Of the possible forms of body the best and most preferable is one which will combine the strongest and most pleasant sound with the most comfort possible in playing. Experience teaches, however, that a guitar will sound both more powerful and pleasant the more the back is arched and the longer the body is as a whole. The most effective form would therefore unquestionably be that of the ancient lutes, theorbos, mandolins and the rest, if this could be established in the regular form of a parabola or an ellipse. This shape would have the added advantage that any question concerning the width of the sides would be removed, there no longer being any sides; rather these would become one with the back.
See also the article “Methods of Construction of Lute and Guitar compared” on this website.