172 Professor C Piazzi Smyth's Meteorological 



The entries of observed quantities being in general made 

 hourly in the log-book, we should have the computed ones 

 also as regularly, and these might be arranged on opposite 

 pages, and exhibited in such a tabular manner, that any after 

 inquirer may see at a glance whether every correction has 

 been duly applied in any particular case ; or may apply, if 

 necessary, more exact corrections to the original observa- 

 tions. These ivill consist of the apparent velocity and direc- 

 tion of motion of the ship, and the same of the wind, and the 

 former will constitute elements of correction for the latter, 

 but must previously be corrected themselves for other ele- 

 ments which should also be inserted in their proper columns, 

 viz. the variation and deviation of the compass, which will 

 of course equally affect the observed direction of the wind, 

 the leeway, and the current. 



Until all these measures are taken, observations on ship- 

 board cannot expect to approach that degree of importance , 

 which, by making these improvements, might so easily be 

 commanded. It has been said that sailors are able, and that 

 they do make the necessary correction by the judgment of 

 their senses, for the effect of this motion of the ship upon the 

 apparent wind felt on board, so as to reduce it to the true 

 wind which would be experienced on a rock at the same place : 

 but that they do not succeed in so doing may be seen most 

 luminously in Lieut. Maury's wind and current charts. Here 

 he has endeavoured to collect together the multitudinous 

 observations of winds and currents made by the greater part 

 of American vessels which have ever sailed, and he has 

 defined the particular strength and direction of the wind as 

 observed on board each ship every day by particular symbols ; 

 a simple inspection of which leads at once in the more 

 regular parts of the world, to a knowledge of the general 

 movements of the atmosphere. Some remarkable anomalies 

 will, however, be found in the region of the trade winds, and 

 at the very part of them too, where such anomalies should 

 not be found, but on examination they are undoubtedly owing 

 to symbols, near each other, belonging to two ships going in 

 different directions, or to one ship changing its course from 

 day to day. The accumulation of multitudes of observations 



