182 



The authoi' next described the problem of determining the true 

 wind from the observed motion of the vessel and the apparent wind, 

 as being merely a special instance of the general theorem of the 

 parallelogram of forces, the course of the ship being one side ; the 

 apparent wind, the diagonal ; and the true wind, another side ; so 

 that the case might always be reduced to the calculation, according 

 to the usual rules for plane triangles, of the third side and one of 

 the anorles of a triangle, from the two other sides of their included 

 angle, excepting in the simpler conditions of going exactly with or 

 against the wind. 



But as the calculations in this way, though easy enough, threat- 

 ened to be uselessly and overpoweringly bui-densome, considering the 

 enormous number of cases which would have to be computed in any 

 voyage, the small degree of accuracy required, and the untoward 

 nature, for trigonometrical calculations, of the data as observed for 

 the ordinary purposes of navigation, — the author contrived a simple 

 set of scales, in which, entering with the directions and velocities of 

 the ship and apparent wind, as usually observed, the direction and 

 velocity of the true wind are given at once by inspection ; and might 

 be insei'ted, with vei'y little trouble to naval officers, in two appro- 

 priate columns introduced into the log-books, as kept at present. 



The following Donations to the Library were announced : — 



First Report on the Coals suited to the Steam Navy. By Sir Henry 

 De la Beche and Dr Lyon Playfair. 8vo. — Bi/ Sir Henry De 

 la Bcche. 



The American Journal of Science and Arts. Conducted by Profes- 

 sors Silliman and Dana. Second Series. January 1848, 

 No. 13. 8vo. — By the Editor. 



Bouet-Villaumez (Le Comte E.) Description Nautique de I'Afrique 

 Occidentale. 8vo. 



Petit-Thouars (Abel du). Voyage auteur du Monde sur la Fregate 

 la Venus. Tom. VI., VII., VIIL, IX., X. (Physique, par 

 U. de Tessan. Tom. I., II., III., IV., V.) 8vo. 

 Atlas Hydrogi-aphique du raeme. Imp. Fol. 



Collection des Cartes des Cotes de France. Imp. Fol. (In sheets.) 



Beyat (P.) Traite de Geodesic a I'usage des Marins. 8vo. 



Expose des Operations Geodesiques. 1839. 4to. 



Beyat. Le meme. 1844. 4to. 



