STORMS, HURRICANES, AND TYPHOONS. 4; 13 



CHAPTER XIX. 



§ 781-808. — STORMS, HURRICANES, AND TYPHOONS. 



781. Plate V. — Plate V. is constructed from data furnished 

 by the Pilot Charts, as far as they go, that are in process of 

 construction at the National Observatory. For the Pilot Charts 

 the whole ocean is divided off into '* fields " or districts of five 

 degrees square, i. e. five degrees of latitude by five degrees of 

 longitude, as already stated in the " Explanation of the Plates.'' 

 Now, in getting out from the log-books materials for showing, in. 

 every district of the ocean, and for every month, how navigators 

 have found the winds to blow, it has been assumed that, in what- 

 ever part of one of these districts a navigator ma^' be when he 

 records the direction of the wind in his log, from that direction 

 the wind was blowing at that time all over that district ; and 

 this is the only assumption that is permitted in the whole course 

 of the investigation. Now if the navigator will draw, or imagine 

 to be drawn in any such district, twelve vertical columns for 

 the twelve months, and then sixteen horizontal lines throuo-h the 

 same for the sixteen points of the compass, ^. e. for N. N.N.E. 

 N.E., E.N.E., and so on, omitting the hy--pomts, he will have 

 before him a picture of the "Investigating Chart" out of whick 

 the " Pilot Charts " are constructed. In this case the alternate 

 points of the compass only are used, because, when sailing free, 

 the direction of the Avind is seldom given for such points as N. 

 hy E., W. hy S., etc. Moreover, any attempt, for the present, at 

 greater nicety would be over-refinement, for navigators do not 

 always make allowance for the aberration of the wind; in 

 other words, they do not allow for the apparent change in tha 

 direction of the wind caused by the rate at which the vessel may 

 be moving through the water, and the angle which her course 

 makes with the true direction of the wind. Bearing this exj^la- 

 nation in mind, the intelligent navigator will have no difficulty 

 in understanding the wind diagram (Plate V.) and in forming a 

 correct opinion as to the degree of credit due to the fidelity with 

 which the prevailing winds of the year are represented on. 

 Plate VIII. As the compiler wades through log-book after log- 

 book, and scores down in column after column, and upon line 

 after line, mark upon mark, he at last finds that, imcler the 



