A reference from the pastWhat is better than reading the same books the Artist, you are studying, read. The great advantage in studying past artists works is the abundance of free texts. In particular in the 17th and 18th century a lot has been published. William Hogarth and his book "The analysis of beauty: written with a view of fixing the fluctuating ideas of taste", Ray Lambert reports, where well known to J. Constable. The book is online here.
PS: a better reprinted version is here.