OCEAN METEOROLOGY. 187 



is evident that all the observations between these lines Avere taken in 

 that square. 



The limits of all the squares traversed are determined and marked 

 in like manner, the number of each square is written between its 

 bounding lines, and, when thus wholly prepared, the observations taken 

 in each square during whatever length of time the ship was in it — 

 whether one hour or several, provided it was continuous time in the 

 same month — are compiled on one blank of Form B. This is a sheet 

 of thick, durable paper, so ruled into columns with appropriate printed 

 headings that each of the following-named items has a place for en- 

 try : the limits in latitude and longitude of the square, its number, 

 and the number of hours the ship was in it ; date of passing through 

 the square, name of the ship, and the period covered by her log-book 

 — all, that direct reference may be had at any time to the original 

 sources. In a series of columns the thirty-two points of the compass 

 are printed in regular order ; blank spaces are provided on the right 

 and left of each point — those on the left for the number expressing 

 the wand's duration from that point, and those on the right for the 

 figure denoting its mean force for the period of that duration. To 

 compile the direction of the wind, the number of hours it w^as from 

 the same point, whether consecutively or at different intervals, are 

 counted, and the sum total is entered on the left opposite the point ; 

 for the force, the mean of the several hourly forces corresponding to 

 the period of direction just mentioned is found and entered on the 

 right of the point. Similarly for each point from which the wind 

 blew while the ship was in the square. 



As the entries regarding the wind in the log-book are hourly esti- 

 mates of both its direction and force, for the hour — an interval that 

 permits little variability in either quantity — accuracy to this degree is 

 insured in both the compilation and charts. There is no averaging the 

 force or direction for longer periods than an hour, and, as far as I am 

 aware, this is the only system pursued by any nation wherein these 

 items are comj^iled with such detail. 



When calms or light, variable airs occur, the number of hours of 

 each is counted, and the sum entered in its proper place. "When a 

 gale — that is, wind of a force of 8 and upward — happens, the number 

 of hours it blew from any of the eight principal points of the compass 

 (supposing it to have varied in direction), together with the force 

 during each period, are duly tabulated. 



The total number of hours of fog, of rain (including snow and 

 mist), and of squalls (heavy, moderate, and light) ; the state of the 

 weather by symbols ; quantity of clear sky ; and variation of the 

 magnetic needle, with the location in which it was observed, are all 

 entered in their respective places. 



The mean of the mercurial barometer, attached thermometer, dry- 

 bulb, wet-bulb, and temperature of the sea-water at the surface — that 



