Synthesized answer
The provided passages do not contain information about the practical implications of the work on the expression of emotions.
The passages only discuss the historical context and existing literature on the subject of expression and physiognomy [1, 2]. They mention that many works have been written on Expression, but more on Physiognomy, and that the author is not concerned with the latter [Passage 1]. The author also notes that older treatises have been of little service, and mentions the "Conferences" by Le Brun as a well-known ancient work [1, 2]. There is no information presented that addresses the practical applications or implications of studying emotional expression.
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.