Lovely quote Gadget.
The Chesterfield letter the diarist is attempting to quote is Letter CXXXVIII LONDON, April 15, O. S. 1751
"MY DEAR FRIEND: What success with the graces, and in the accomplishments, elegancies, and all those little nothings so indispensably necessary to constitute an amiable man? Do you take them, do you make a progress in them? The great secret is the art of pleasing; and that art is to be attained by every man who has a good fund of common sense. If you are pleased with any person, examine why; do as he does; and you will charm others by the same things which please you in him. To be liked by women, you must be esteemed by men; and to please men, you must be agreeable to women. Vanity is unquestionably the ruling passion in women; and it is much flattered by the attentions of a man who is generally esteemed by men; when his merit has received the stamp of their approbation, women make it current, that is to say, put him in fashion. On the other hand, if a man has not received the last polish from women, he may be estimable among men, but will never be amiable. The concurrence of the two sexes is as necessary to the perfection of our being, as to the formation of it. Go among women with the good qualities of your sex, and you will acquire from them the softness and the graces of theirs. Men will then add affection to the esteem which they before had for you. Women are the only refiners of the merit of men; it is true, they cannot add weight, but they polish and give lustre to it.
‘A propos’, I am assured, that Madame de Blot, although she has no great regularity of features, is, notwithstanding, excessively pretty; and that, for all that, she has as yet been scrupulously constant to her husband, though she has now been married above a year. Surely she does not reflect, that woman wants polishing. I would have you polish one another reciprocally. Force, assiduities, attentions, tender looks, and passionate declarations, on your side will produce some irresolute wishes, at least, on hers; and when even the slightest wishes arise, the rest will soon follow."
https://www.gutenberg.org/files/3361/3361-h/3361-h.htm
