What is the 'exact quality' here?
'COME up to town with me and see Ross,' Walter said at breakfast next morning.
But Searle wanted to stay in the country. It was blasphemy, he said, to spend even one day in London with the English countryside bursting into its first green. Besides, he did not know Ross. It would be better if Walter put the proposition to Ross first, and brought him into the business later.
And Walter, though disappointed, did not stop to analyse the exact quality of his disappointment.
(Chapter 5 To Love and Be wise, http://gutenberg.net.au/ebooks08/0800551h.html#ch05)

Does it mean the reason?

Question

What is the 'exact quality' here?
'COME up to town with me and see Ross,' Walter said at breakfast next morning.
But Searle wanted to stay in the country. It was blasphemy, he said, to spend even one day in London with the English countryside bursting into its first green. Besides, he did not know Ross. It would be better if Walter put the proposition to Ross first, and brought him into the business later.
And Walter, though disappointed, did not stop to analyse the exact quality of his disappointment.
(Chapter 5 To Love and Be wise, http://gutenberg.net.au/ebooks08/0800551h.html#ch05)

Does it mean the reason?

Answer

"exact quality" means the "exact nature" of something. In this case "his disappointment." So you could then rephrase it to say: "Walter, though disappointed, did not stop to analyse how exactly how disappointed he was."