NAVIGATION. 45 



" The log-line is divided into equal portions 

 called knots, at each of which a bit of string, with 

 the number of knots upon it, is put through the 

 strands. 



" The length of a knot depends on the number 

 of seconds which the glasses measure, and is thus 

 determined : 



" No. of ft. in I knot : No. of ft. I m. : : No. of sees, of the glass : 

 3600 (No. of seconds in an hour). 



" The nautical mile being about 6080 feet, we 

 have, for the glass of 30 seconds, the knot 

 = (6080 x 3o)/36oo = 507 feet, or 50 feet 8 

 inches ; for the glass of 28 seconds, the knot 

 = (6080 X 28)/36oo = 47*3 inches, or 47 feet 

 4 inches, and so for any other glass. 



"The log-line should be repeatedly examined, 

 by comparing each knot with the distance between 

 the nails, which are (or should be) placed on the 

 deck for this purpose at the proper distance. The 

 line should be wet whenever it is required thus 

 to remeasure it, or to verify the marks. 



"As the manner of heaving the log must be 

 learned at sea, it is only necessary to remark, for 



