VOL. LXXI.] PHILOSOPHICAL TRANSACTIONS. 25 



laid floor of seasoned wood opened sufficiently to lay one's finger in them ; but 

 become as close as before on the ceasing of the harmattan. The seams also in 

 the sides and decks of ships are much injured, and the ships become very leaky, 

 though the planks are 2 or 3 inches in thickness. Iron-bound casks require the 

 hoops to be frequently driven tighter; and a cask of rum or brandy, with 

 wooden hoops, can scarcely be preserved ; for, unless a person attends to keep 

 it moistened, the hoops fly off. 



The parching effects of this wind are likewise evident on the external parts of 

 the body. The eyes, nostrils, lips, and palate, are rendered dry and uneasy, 

 and drink is often required, not so much to quench thirst, as to remove a painful 

 aridity in the fauces. The lips and nose become sore, and even chapped; and 

 though the air be cool, yet there is a troublesome sensation of prickling heat on 

 the skin. If the harmattan continues 4 or 5 days, the scarf skin peels off", first 

 from the hands and face, and afterwards from the other parts of the body, if it 

 continues a day or two longer. Mr. Norris, who frequently visited the coast of 

 Africa, observed, that when sweat was excited by exercise on those parts which 

 were covered by his clothes from the weather, it was peculiarly acrid, and tasted, 

 on applying his tongue to his arm, something like spirit of hart's-horn diluted with 

 water. 



As the state of salt of tartar placed in the open air, and the quantity evapo- 

 rated from a given surface of water, are obvious proofs of the comparative mois- 

 ture or dryness of the atmosphere, Mr. Norris put the harmattan to each of 

 these tests; and particularly to moisten salt of tartar ad deliquium, and exposed 

 it to the night air during the time that the harmattan was blowing. The follow- 

 ing is the account of the result of these experiments. Salt of tartar will not 

 only remain dry during the night as well as in the day; but, when liquefied so 

 as to run on a tile, and exposed to tie harmattan, becomes perfectly dry in 2 or 

 3 hours; and, exposed in like manner to the night air, will be dry before 

 morning. 



It appears, from experiments made by Mr. Norris, that if the evaporation of 

 the whole year be supposed to go on in the same proportion with what occurred 

 during a short and very moderate return of the harmattan, the annual harmattan 

 evaporation would be 133 inches; and if the calculation was made in proportion 

 to the evaporation which occurs during a longer visit from the harmattan, and a 

 more forcible breeze, the annual harmattan evaporation would be much more 

 considerable. If the annual evaporation be in like manner calculated, in pro- 

 portion to the evaporation which took place subsequent to and preceding the 

 harmattan, the annual evaporation at Whydah on the Gold Coast, would be 64 

 inches, and he had found the annual evaporation at Liverpool to be 36 inches. 



VOL. xv. E 



