VOL. XXXVI.] PHILOSOPHICAL TRANSACTIONS. SSQ 



in any motion of the boat, tiie bars are accordingly afFected. This instrument 

 is so contrived, that two of the flyers on one side always resist the water in the 

 motion of the vessel, while the other two give way in their turning. The 

 resisting flyers in this figure are a and b, and d and c will be the same when 

 they come into their position ; for they resist and give way alternately so long 

 as the motion continues, which is always circular ; and so truly does it revolve, 

 that be the motion swift or slow, in any measured distance, the number of re- 

 volutions will be equal. 



But considering, that though this projection might be serviceable in barges, 

 pleasure-boats, or other vessels, in fair and moderate gales of wind, yet it 

 might prove useless in boisterous and stormy weather, and in long voyages, 

 when it might be choaked with weeds ; Mr. S. therefore fixed to liis other in- 

 vention the fork, which is contrived in such a manner, that it will determine 

 the ship's way in a storm, or when she is scudding before the wind, when the 

 log is incapable of it. 



Fig. 3. shows the fork in 3 different positions, or motions of the vessel. This 

 needs no explanation, for it plainly appears, that the pallets will be more or less 

 afFected by the resistance of the water, according to the position they are in; 

 and therefore the revolutions in a swift or slow motion, in the same distance, 

 cannot be equal, as had been represented by Dr. Desaguliers, Mr. Samuel 

 Molyneux, and Mr. Gravesande. 



Being now fully persuaded that the fork would not revolve equally in the 

 same distance, and in different motions of the vessel, Mr. S. now began to re- 

 pair this defect by calculating some tables, which render it still a very useful 

 instrument. 



Fig. 4 shows a further improvement, in which the objections of the different 

 inclinations of the fork are now entirely removed, afgh is the fork, in the 

 same form as the iron fork described in the Philos. Trans. Vol. xxxiii, which 

 differs from the other only in the materials of which it is framed ; this being 

 contrived of such as to make it equiponderous with the water, and to lie in an 

 horizontal position in all cases, hb is a rope, of a convenient length, fixed to 

 a screw or worm at the point b, which goes about 6 inches into an iron pipe, of 

 which Bi is the length : through this pipe an iron spindle passes into the screw 

 or worm to which the dial c is fixed. As soon then as the vessel moves, the 

 fork plays in a horizontal position, which moving the spindle within the iron 

 pipe, the motion is communicated to the dial, which is fitted to strike to the 

 miles or leagues the vessel runs. And whether the vessel move swift or slow, 

 the pallets a and f are equally affected, and consequently must measure the 

 X X 2 



