OCEAN METEOROLOGY. 189 



could be obtained relative to the expanse of ocean under consideration, 

 the next step is to classify these, and to reduce the observations. The 

 classification consists in grouping together all the sheets of the same 

 square for the same month, without distinction as to year or ship ; 

 and, to reduce, all the observations on the blanks of each group are 

 first transcribed to a single sheet of another blank, Form D — a kind 

 of ledger, as it were, to which the separate sheets of Form B bear the 

 relation of so many entries in a day-book. 



It may not be entirely devoid of interest to some of my readers, to 

 have here such a description of Form D as will enable them to repro- 

 duce it : a fac-simile before one would render the details of the reduc- 

 tion more easily intelligible. 



At the top of the form are spaces for entering the number of the 

 square and the name of the month. Under this are six vertical col- 

 umns crossed by thirty-four horizontal lines. The headings of the 

 columns in succession, from the observer's left to right, are as follows : 

 1st column, " Total No. of hours of wind from every alternate point " ; 

 2d, " No. of hours of wind from every point " ; 3d, " True direction 

 of wind" (under this heading the points of the compass, beginning 

 with north, are printed — one point on each line — down the first thirty- 

 two lines of the blank, and " calms " and " variable wdnds " are on the 

 last two lines ) ; 4th, " Mean force of wind from every point " ; 5th, 

 " Final mean force of wind from every alternate point " ; and, 6th, 

 " Percentage of wind from every alternate point." 



To illustrate the use of Form D, suppose that for any square for 

 any month — say No. 643 for July — there are fifty sheets of Form B. 

 To collect the numerous observations of the wind scattered through- 

 out these, each point is considered separately and in succession. The 

 sum of the different periods that the wind was of the same force from 

 the same point on all the sheets of Form B is found ; the direction of 

 the wind on this Form being magnetic, it is corrected for the varia- 

 tion of the compass, and then the sum is entered on Form D opposite 

 that point w^hich it becomes as a true direction. 



Take a specific case, and let it be the magnetic north of Form B, 

 with the variation one point westerly for the square under reduction : 

 suppose that all the hours the wind was a force of 5 amounted to 80 ; 

 then " 80 " would be entered in the 2d column, and " 5 " in the 4th 

 column of Form D, on the horizontal line on which " N. by W." is 

 printed ; because a magnetic north wind becomes a true north-by- 

 west wind when the variation is applied. Again, if all the hours the 

 wind was of another force, say 3, from the same point (magnetic 

 north) amounted to 120, then " 120 " would be placed in the 2d col- 

 umn, on the right of the previous sum 80, and " 3 " in the 4th column, 

 on the right of the other force, 5. Similarly, with all the hours of 

 each force, and with every point of the compass, the order being pre- 

 served throughout of havinor the first sum of hours in the 2d column 



