OCEAN METEOROLOGY. 



193 



squalls and gales. The figures between the middle and the inner circle 

 denote the percentage of wind from every alternate point : thus, of the 

 1,110 hours of observation, the wind was 20 per cent, of the time from 

 the K TV. ; 8 per cent, from N. N. W. ; 3 per cent, was calm ; and 

 one per cent, light variable winds. The little table below the number 

 of the square is to be read thus : of the 1,110 hours, 30 were calm ; 

 10 were characterized by light airs flying all round the compass ; no 

 fog ; 9 hours were rainy ; no heavy squalls ; and no light squalls. In 

 the upper left-hand corner is the mean of the barometer, 30-05 — the 

 mean of all the hourly observations taken in the square during the 

 month ; under it is the mean daily range, 0*09 inch — the mean of the 

 differences between the daily maxima and minima for 46 days. In the 

 upper right-hand corner, under D. B. (dry-bulb) is the mean tempera- 

 ture of the air (in the shade), 80° Fahr. ; the 5° under it is the mean 

 daily range, both means obtained as for the barometer. Similarly, in 

 the lower right-hand corner, is the mean temperature of evaporation 

 and its daily range ; and, in the lower left-hand corner, the mean tem- 

 perature of the sea-water at the surface and its mean daily range. 



The remarks within the circles are drawn from the experience of 

 all the vessels that passed through the square in all the months of the 

 year. It is their aim to fill up the outline character of the square 

 afforded by the figures. While these remarks run through all the 

 squares that have sufficiently similar features to be described together, 

 the figures are applicable only to the square and month in which they 

 appear. Thus are the climatic features of each small area of ocean de- 

 lineated. 



It should be understood that these charts merely exhibit the ex- 

 perience of the past reduced to a scale of probabilities for the future : 

 if, then, the conditions stated in any square be not exactly realized, 

 the system should not hence be condemned. 



Let any navigator consider the degree of dependence he will place 

 on a trustworthy record of a passage he once made ; the confidence 

 with which he will refer to that record — to the experience of a single 

 voyage ! — for his guidance in traversing the same ground again : now, 

 it is not the record of one passage alone, but of many — all conveniently 

 arranged, with every discernible error and inaccuracy eliminated— that 

 is given in any square of these charts. 



As a fair way of regarding them, let us consider the data of the 

 square 106 : of the 1,110 observations of the wind, it was 226 hours, or 

 20 per cent, of the whole time, from the N". W. ; hence, at any future 

 time, there are twenty chances for a N, W. wind of a force of 3, against 

 eight for a N. K W, wind, force 2 ; against seven for a N, wind, 

 force 3 ; against three for calms and one for very light airs. 



The observations of the direction of the wind on Maury's pilot 

 charts have been incorporated with those extracted from log-books and 

 journals of recent date, and, although they outnumber the latter, still 



VOL. XVI. 13 



