The naval review at Spithead, upon the close of the Crimean war in 1856, was the greatest up to that time. Ten vessels out of two hundred and fifty still had not steam power, but almost all the others were propelled by the screw--the spiral oar of Watt's letter of 1770--a red-letter day for the inventor. Watt's early interest in locomotive steam-carriages, dating from Robison's having thrown out the idea to him, was never lost. On August 12, 1768, Dr. Small writes Watt, referring to the "peculiar improvements in them" the latter had made previous to that date. Seven months later he apprises Watt that "a patent for moving wheel-carriages by steam has been taken out by one Moore," adding "this comes of thy delays; do come to England with all possible speed." Watt replied "If linen-draper Moore does not use my engine to drive his chaises he can't drive them by steam." Here Watt hit the nail on the head; as with the steamship, so with the locomotive, his steam-engine was the indispensable power. In 1786 he states that he has a carriage model of some size in hand "and am resolved to try if God will work a miracle in favor of these carriages." Watt's doubt was based on the fact that they would take twenty pounds of coal and two cubic feet of water per horse-power on the common roads. Another of Watt's recreations in his days of semi-retirement was the improvement of lamps. He wrote the famous inventor of the Argand burner fully upon the subject in August, 1787, and constructed some lamps which proved great successes. The following year he invented an instrument for determining the specific gravities of liquids, which was generally adopted. One of Watt's inventions was a new method of readily measuring distances by telescope, which he used in making his various surveys for canals. Such instruments are in general use to-day. Brough's treatise on "Mining" (10th ed., p. 228) gives a very complete account of them, and states that "the original instrument of this class is that invented by James Watt in 1771." In his leisure hours, Watt invented an ingenious machine for drawing in perspective, using the double parallel ruler, then very little known and not at all used as far as Watt knew. Watt reports having made from fifty to eighty of these machines, which went to various parts of the world. In 1810 Watt informs Berthollet that for several years he had felt unable, owing to the state of his health, to make chemical experiments. But idle he could not be; he must be at work upon something. As he often said, "without a hobby-horse, what is life?" So the saying is reported, but we may conclude that the "horse" is here an interpolation, for the difference between "a horse" and "a hobby" is radical--a man can get off a horse.