liOi/cd Society of LondoTU 273 



by rarefaction. The reverse is the case on land ; as no cur- 

 rent of wind can pass many miles without experiencing a 

 change of temperature, density, velocity^ and even direc- 

 tion, in consequence of the variegated surface and tempe- 

 rature of the earth. The rencounter of two opposite cur- 

 rents of wind, at sea, docs not produce the effect proper 

 to solid bodies in motion, according to the received laws of 

 mechanics; on the contrary, as their temperatures and den- 

 sities must necessarily be different, each pursues its unde- 

 viating course without any change, excepting only that the 

 least dense is obliged to ascend and make room for the other, 

 which keeps next to the surface of the water j notwithstanding 

 which, each proceeds with nearly its original velocity. Two 

 currents of air, whatever may be their temperatures or den- 

 sities, never incorporate either by sea or land, without the 

 intervention of a third body (such as mountains, &c.), which 

 destroys their respective velocities. No such resisting bodies 

 being at sea, the different currents of wind must consequently 

 follow the law of their densities. Parallel currents often 

 occur in very short distances, and the intervening spaces 

 frequently experience dead calms, sometimes accompanied 

 with fogs, or with unclouded brightness, and considerable 

 heat. This circumstance will, on many occasions, account 

 either for the stagnancy or rapid fluctuation of the mercury 

 in the barometer at sea; v.hich can never happen, even in the 

 warmest or most electrical climates, on shore, where there 

 is a much greater and more general sameness of density and 

 temperature in the atmospherical currents, in consequence 

 of the greater facilities of commixtion, and often, indeed, 

 of chemical union of the different gases. 



For these remarks, which form no part of captain Flin- 

 ders's communication, we arc indebted to a gentleman who 

 has made a number of observations on this important sub- 

 ject. Should any df our nautical readers, or others who 

 may have had an opportunity of making similar observa- 

 tions, communicate to us the result of their experience *j 

 we shall gladly lend our aid to the collecting of such facts 



• AJdtcssed to the Editor of The Philoiophical Magazine. 

 Vol. 64. No. 95. JprlllBOG* S 9M 



