N D I X. 



Observations on different Methods of meafurlng a 



Ship's Way. 



*" I ^ H E degree of accuracy with which the diftance run 

 •*" by a fhip can be meafured, is a thing of great im- 

 portance, but unfortunately not eafily to be afcertained, 

 from the great variety of circumftances which may oc- 

 cafion errors in the reckoning, and which, though not 

 depending upon the meafure of the fhip's way, may in 

 voyages not nearly upon a meridian be confounded with 

 thofe that do. The circumftances of the prefent voyage 

 gave me the faireft opportunity of trying this experiment, 

 the weather being fine, and the courfe very nearly upon 

 a meridian ; fo that an error of one point could not make 

 more than the difference of one mile in fifty in the 

 diftance. When the difference of latitude is the fame as 

 the diftance, it gives frequent opportunities of comparing 

 the reckoning with the obfervation, and whatever error is 

 found muft be attributed to the imperfedions in the 

 manner of meafuring the diftance. Moft of the writers on 

 this fubjed have attributed the errors to a faulty divifion 

 of the log-line. 



Before Norwood meafured a degree, the length of a 

 minute had been erroneoufly fuppofed 5000 feet; in 



P confequence 



87 



