On the Sublime and Beautiful/Part IV/Chapter 20
IT is to explain the true cause of visual beauty, that I call in the assistance of the other senses. If it appears that smoothness is a principal cause of pleasure to the touch, taste, smell, and hearing, it will be easily admitted a constituent of visual beauty; especially as we have before shown, that this quality is found almost without exception in all bodies that are by general consent held beautiful. There can be no doubt that bodies which are rough and angular, rouse and vellicate the organs of feeling, causing a sense of pain, which consists in the violent tension or contraction of the muscular fibres. On the contrary, the application of smooth bodies relaxes; gentle stroking with a smooth hand allays violent pains and cramps, and relaxes the suffering parts from their unnatural tension; and it has therefore very often no mean effect in removing swellings and obstructions. The sense of feeling is highly gratified with smooth bodies. A bed smoothly laid, and soft, that is, where the resistance is every way inconsiderable, is a great luxury, disposing to an universal relaxation, and inducing beyond anything else that species of it called sleep.