Synthesized answer
The author mentions consulting older treatises on Expression and Physiognomy, finding the older treatises to be of little service [1]. He notes that the famous "Conferences" by the painter Le Brun, published in 1667, is the best-known ancient work and contains some good remarks [1, 2].
The provided passages describe the author's initial research into existing works on Expression and Physiognomy. However, they do not detail the specific evidence the author provides to support his own theories or arguments regarding the expression of emotions.
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
Title: The expression of emotions in man and animals by Charles Darwin Description: Many works have been written on Expression, but a greater number on Physiognomy, - that is, on the recognition of character through the study of the permanent form of the features. With this latter subject I am not here concerned. The older treatises,[1] which I have consulted, have been of little or no service to me. The famous `Conferences'[2] of the painter Le Brun, published in 1667, is the best known ancient work, and contains some good remarks.