VOL. XXXIII.l PHILOSOPHICAL TRANSACTIONS. 127 



within the ship or vessel. This rope may be about 5 fathoms, more or less, 

 according as the dial is fixed high or low, in respect to the surface of the 

 water. 



In the figure this machine has but two branches; however, it maybe formed 

 of three, if not four, and adjusted to the same standard or measure; but as 

 three or four branches would be more subject to entangle in sea-weeds, and so 

 prevent the regular motion of the instrument, if not in some measure impede 

 the ship's way, Mr. S. approves of two only; for, in an experiment at sea, he 

 observed those made in this form have been so far from being choaked by 

 weeds, that if they encountered any, they always cleared themselves again, 

 without the trouble of hauling the engine into the ship to do it. 



This instrument may be regulated several ways: first, by opening or closing 

 the angle ced; secondly, by lengthening or shortening the brandies, or turning 

 or bending more or less the pallets akcl and bhdi; by which the machine is 

 brought to any standard or measure, to cause the hydraulical revolution to 

 answer either to a geometrical pace of 5 feet, or to 10, 12, 14 feet, &c. 



The machines of this kind, which he tried at sea, in all sorts of weather, 

 weighed some 4, others 5, and others 6 pounds ; their weight not at all affect- 

 ing the peculiar property of the instrument, nor hindering the regulation of 

 them. They may be made of tin, as well as iron, and so light as not to weigh 

 above 2 or 3 lb. which may serve for any boat, wherry, barge, &c. without any 

 hindrance to their rowing or sailing. The manner of fixing them to a ship or 

 boat is represented in fig. 2. 



Mr. S. explains three several dials, any one of which may be used with this 

 machine. The first had three indexes, one of which marked ten revolutions 

 of the engine, each revolution 10 feet; so that the whole round of the circle 

 was 100 feet. As five of these revolutions make 50 feet, by holding the half- 

 minute glass in one's hand, which is always used with the log-line, by inspec- 

 tion is seen how many times 50 feet the ship runs in half a minute, and of 

 course how many miles an hour, without the trouble of employing four or five 

 persons as usual in heaving the log. The second index on this dial marked 100 

 revolutions, which makes 1000 feet, as the third index did 1000 revolutions, 

 which is equal to 10,000 feet; and then a little bell struck, signifying when 

 the ship had sailed that distance, which may be also fitted to strike to any other 

 measure. 



The second dial had the circle on its plane divided into 12 parts; so that as 

 the index passed each division, the ship had run 1 mile, and consequently 12 

 miles when it had measured the circumference. On one side of this dial was 



