DIURNAL OSCILLATIONS OF THE BAROMETER. 33 



Now, the fact of the barometer showing a less 

 amount of atmospheric pressure in the southern than 

 in the northern hemisphere, we have already men- 

 tioned as being in accordance with what we should 

 expect in case of a motion of the solar system in the 

 direction of the south pole, notwithstanding there 

 being a greater mass of air over the southern than 

 over the northern hemisphere, for the force of 

 attraction which draws the air so as to form a tide in 

 the southern hemisphere tends to prevent downward 

 pressure upon the barometer; whereas the force of 

 vis inertiae which, by means of converging currents, 

 forms a tide in the northern hemisphere, tends by 

 the pressure of those converging currents to cause 

 increased pressure upon the barometer. 



And, the annual oscillation of pressure backwards 

 and forwards between the northern and the southern 

 hemispheres, which is shown by the table on p. 29, 

 we mentioned as being in accordance with what we 

 should expect from effects of attraction and vis 

 inertia precisely analogous to the foregoing, seeing 

 that the northern and southern hemispheres are alter- 

 nately in advance in the orbital motion of the earth. 

 If such be the cause of the difference in atmospheric 

 pressure in the northern and southern hemispheres; 

 and of the annual oscillation of pressure between the 

 two hemispheres : then the diurnal oscillation of pres- 

 sure shown by the table opposite is precisely such as 

 we should naturally expect under the action of the 



VOL. II. D 



