NEW METHOD OF MEASURING A SHir's VELOCITY. $J 



X. 



,New Method proposed for measuring a Ship's Rote of Sail- 

 ing. By the same Gentleman. 



Line towing astern of a vessel, which is passing a line towed 



through the water, will pull against her bead-way. As the a^emofaship 

 o ' r ° ... Will be a pep« 



ship's way increases., the pull of the line will increase; and petuid log. 



vice versa. If this, with a proper scope of line (about 25 

 fathoms may probably be sufficient) shall be found to be a 

 regulated quantity of pull corresponding in the same man- 

 ner at all times to the rate of sailing, it will answer the pur- 

 pose of a log. Many experiments have been made upon 

 the same principle ; but the most plain and easy one, of 

 towing a measured length of line, has escaped trial; though 

 less liable to give erroneous or variable results than any 

 which can be made near a ship. By it, the rate of sailing 

 may be obtained either constantly or occasionally, and can 

 be taken with ease by one person: in which respect it would 

 have great advantage over the common log, the use of which 

 requires three persons. 



By a trial made in a boat with about 20 fathoms of line, Experiment, 

 rather larger than log line, towing astern and fastened to a 

 spring steelyard, the strength of the pull was found to vary 

 with the rate of sailing, which however was not ascertained 

 by measurement; but by estimation, the boat's rate of sail- 

 ing during the trial varied between 2| knots and 5 knots per 

 hour, and the pull of the line upon the steelyards was ob- 

 served to vary from 2 lbs. to 5flbs. ; increasing and de- 

 creasing with the velocity. So great a variation in the 

 strength of the pull gives all the advantage, which can be 

 desired for forming a scale, and will allow of the experiment 

 being made with smaller line. 



If the proposed length of line is passed through a pulley The velocity 

 so as to go clear out at the stern port or cabin window, and indicated by 

 the inner end is fastened to a loose chain, of weight adapted 

 to the purpose, on the deck under the pulley ; or to a num- 

 ber of small weights made consecutive by short intervals of 

 line, the chain or weights will be drawn up more or less ac- 

 cording 



