As a non-horsey person, I need to ask what is the nature of the “straps” referred to in this letter?
“Lt Col. Rowley, was oblivious of straps, and presented an expanse of rather ill-blacked, calfskin boot that took away from his military ensemble a good deal. When a man can ride without straps, he may do so, if he chooses; but, when he possesseth not the happy faculty of keeping down his trowsers, he should make straps a part of his religion!”
If I were to guess, they sound like some sort of "reverse garter" to keep the pants leg from riding up. But their mechanics elude me.