Thus it was that when, early in the first week, Venning said he had an idea for a boat that could be easily carried round the cataracts and worked without much labour, he was at once encouraged to give plans and specifications.

“I read once about a ’sneak-box’—­a flat-bottomed shooting canoe—­ that could carry a sail and serve at the same time as a cabin.”

“I have used one myself duck-shooting.  Go on.”

“Well, sir, I built a boat on the plan given, and spent a holiday one year on the Broads.  It drew very little water, and was easily managed.  However, you know all that.  But what I was thinking about was a design for a larger boat of the kind, with a propeller attached to it which could be worked by lever.”

“By a lever?”

“Perhaps you have seen a lame man working a bicycle by a lever—­ well, after that principle.  There would be a steel rod with cog-wheels, and one man could work the lever as the lame cyclist does without the labour of rowing.”  Venning waited nervously for the criticism.

“At any rate the lever would be a relief after the paddles,” said Mr. Hume, gravely.

“But that is not all,” continued the inventor, hastily.  “I would rig up a light American windmill amidships, which could work the screw and get more speed with a following wind in conjunction with a sail rigged up forward.”

“Bravo, my boy!” said Mr. Hume, laughing.  “How many revolutions of the screw to the minute do you expect to get out of your windmill?”

“That depends on the power of the wind, sir.  Do you think it is a mad scheme?”

“It would impress the natives,” said Compton, “and at any rate we could start wheat-milling, you know, in case we came to the end of our resources.”

“There’s no wheat in Central Africa, you duffer!  Besides, sir, it’s mainly a question of gear.  With a lever, cog-wheels, and a running chain after the pattern of the cycle chain, one could——­”

“And ball bearings,” suggested Compton, slyly.

“Yes; and ball bearings—­the friction would be reduced, and we could get more power out of a screw and propeller than we could from four paddles.”

“You may be right,” said Mr. Hume, thoughtfully.

“We don’t want to take a large party, and I confess the water transport has bothered me very much.  The wind-mill, I am afraid, we must leave to some other time, but the other part of your scheme is worth placing before practical men, and I will give you a letter to a friend of mine who had a boat built on the Thames.”

Venning saw the friend the very next day; the friend gave him an introduction to a member of a great firm of torpedo-boat builders on the Thames, and this gentleman very kindly gave the matter five minutes’ attention.

“Your idea, eh?” said the great designer.  “Explain what advantage you expect to gain.”

“Less labour in working than with paddles, and greater speed.”