“‘_December 21st, 1817._—I also wish to make a model of a boat to be driven by pumping [in] water at the prow and forcing it out at the stern. This is an idea of my father’s; and I think it will obviate the objection against driving canal boats by machinery, which is that the paddles agitate the water to such a degree as to injure the sides of the canal’ “A few years later I set down another first conception, this time of my own, which, however, I never carried further. The record is as follows:— “‘Steam vessels might be propelled by means of an endless screw, something like a corkscrew with the wire flattened in a direction perpendicular to the axis. There might be several fixed at the sides, at the stern, &c. This apparatus would work equally well whether altogether or partly immersed in water. If one could be placed so as to move like a rudder, it would be exceedingly efficient in changing the direction of the boat.’”[37] I find also in his Journal for the year 1817, the following record: “If I can find time, I intend to construct a model of an engine which I have long thought of. It is something similar to a steam-engine, only that it is to work by exploding a mixture of hydrogen and oxygen gases. Such an engine I think might be employed to advantage in driving carriages, as the gases might be condensed.” A few months later he writes: “During the Christmas vacation I tried a few experiments to ascertain the force of exploded oxygen and hydrogen when in combination, and found it to be so small that it cannot be applied to the purpose I intended; at least, that such an engine would be far more expensive than one to work by steam.” Soon after he had finished his clock he undertook a very different piece of work. He had already taught himself the art of land-surveying. “I learned the art,” he wrote, “as best I could; I might almost say I found it out, for I had then no book on the subject, and my father had no special knowledge of the matter.” As was usual with him, he at once began to teach what he himself had learnt. With a class he measured and mapped the playground and some little of the neighbourhood. About this time a murder—famous in legal history—was committed within four miles of Hill Top, and at once roused a strong public interest.