Chapters 13-18

Is this not a study of extremes? Initially Passepartout is a bit indifferent to Fogg. Then he slowly begins to warm toward him because "slowly" is how Pass thinks! One of the few times PF gingerly slips out of his comfort zone to save a bonny lass because he has the time and Pass goes nuts In Chapter XIII "His master's idea charmed him; he perceived a heart, a soul, under that icy exterior. He began to love Phileas Fogg". I personally don't see a heart or soul; I think PF is just a little bored and doesn't have any whist partners handy. However, the suttee is a bit bizarre, isn't it? I don't think I would want to get out and view the Ganges if I was traveling it. Why not just go into the restaurant, order a Pepsi and look at some postcards?
Mr. Oysterpuff? How contrived. But a classic quote
"The first case," said he. Then, putting his hand to his head, he exclaimed, "Heh! This is not my wig!"
"No, your worship," returned the clerk, "it is mine."
"My dear Mr. Oysterpuff, how can a judge give a wise sentence in a clerk's wig?"

How indeed?

Are the personalities and sentiments of Phileas and Passepartout juxtaposed against one another to draw attention to their dissimilarities?

I hate to say this, but I think Verne is just having some fun.