Turning of the Wind. Ill 



If the phenomena Ave observe with the weather vane are in 

 their principal features the result of two contending currents 

 of air, namely, the equatorial and the polar currents, it is a 

 matter of necessity that the various meteorological instru- 

 ments should be differently affected by the prevailing proper- 

 ties of those currents. 



The polar current coming from the antarctic regions must 

 be cold, dense, and dry. The equatorial, on the contrary, com- 

 ing from the belt of calms, must be warm, light, and moist. 



The barometer will therefore stand high with the polar 

 current and low with the equatorial. 



The thermometer will be low with the polar current and 

 high with the equatorial. 



The tension of aqueous vapour will be slight with the polar 

 current and great with the equatorial. 



The different intermediate winds* will, of course, have cor- 

 responding influences on the meteorological instruments. 



It is necessary that we call to mind the different principles 

 of the law, and that we thoroughly understand the illustrious 

 savant who founded these theories, when he says, " a south- 

 east wind comes further from the south than the south wind 

 itself." The amount of deflection offers a criterion as to the 

 difference in latitude between the place of observation and 

 the point whence the current of air comes, and certainly the 

 S.E. being more deflected than the S., must have more of the 

 qualities of the polar current than the S. With S.E. wind 

 Ave should have the highest barometer, the lowest temperature, 

 and the least tension of aqueous A'apour. As the wind recedes 

 from this point, the barometer begins to fall, the thermometer 

 to rise, and the tension of aqueous vapour to increase, in 

 consequence of the approaching equatorial current. 



Analogously to the conclusions Ave arrived at with regard 

 to the polar current, Ave might expect that the lowest state of 

 the barometer, and the maximum of temperature and aqueous 

 pressure would coincide with N.W. ; thus the extremes of 

 the phenomena are given, and between them the instruments 

 must shoAv regular curves. For the purpose of illustrating 

 these facts, I could have used the results of yearly observa- 

 tions, but I content myself Avith laying before you those of 

 but one month, and for this purpose I again selected the 

 month of April, 1859, because the means of the pressure of 

 air, and of aqueous vapour, and of temperature of air, nearly 

 coincide Avith the mean values for the year, viz. : 29 '881 

 inches, 0365 inch, and 58 - 3 degrees. 



