Another remarkable instance of Franklin's passion for investigation is afforded in the following interesting letter to Sir John Pringle: "When we were travelling together in Holland, you remarked that the canal boat in one of the stages went slower than usual, and inquired of the boatman what might be the reason; who answered that it had been a dry season, and the water in the canal was low. On being asked if it was so low that the boat touched the muddy bottom, he said no, not so low as that, but so low as to make it harder for the horse to draw the boat. We neither of us at first could conceive that, if there was water enough for the boat to swim clear of the bottom, its being deeper would make any difference. But as the man affirmed it seriously as a thing well known among them, and as the punctuality required in their stages was likely to make such difference, if any there were, more readily observed by them than by other watermen who did not pass so regularly and constantly backwards and forwards in the same track, I began to apprehend there might be something in it, and attempted to account for it from this consideration, that the boat in proceeding along the canal must, in every boat's length of her course, move out of her way a body of water equal in bulk to the room her bottom took up in the water; that the water so moved must pass on each side of her, and under her bottom, to get behind her; that if the passage under her bottom was straitened by the shallows, more of the water must pass by her sides, and with a swifter motion, which would retard her, as moving the contrary way; or that, the water becoming lower behind the boat than before, she was pressed back by the weight of its difference in height, and her motion retarded by having that weight constantly to overcome. But, as it is often lost time to attempt accounting for uncertain facts, I determined to make an experiment of this, when I should have convenient time and opportunity. "After our return to England, as often as I happened to be on the Thames, I enquired of our watermen whether they were sensible of any difference in rowing over shallow or deep water. I found them all agreeing in the fact that there was a very great difference, but they differed widely in expressing the quantity of the difference; some supposing it was equal to a mile in six, others to a mile in three. As I did not recollect to have met with any mention of this matter in our philosophical books, and conceiving that, if the difference should be really great, it might be an object of consideration in the many projects now on foot for digging new navigable canals in this island, I lately put my design of making the experiment in execution, in the following manner.