68 Transactions. — Miscellaneous. 



parallel of latitude is below the average, and that the high 

 barometer, or greater atmospheric pressure, there is due to the 

 downward motion of the air rather than to the greater height 

 of the column of air. Similarly it ma.y be that the compara- 

 tively low barometer near the equator, and the very low baro- 

 meter near the antarctic and arctic circles and in the centres 

 of rotating storms, may be due to ascending currents of air 

 there rather than to a lower level of the surface of the atmo- 

 sphere. Should this be as 1 suppose — namely, that the 

 general level of the surface of the atmosphere is higher at the 

 equator and towards the poles than it is near the 35th parallel 

 of latitude — the circulation would take place, as we know it 

 does, according to the laws of gravity. The velocity acquired 

 by the air sliding down two inclined planes from the equator 

 and polar regions and meeting about the 35th parallel would 

 produce the downward movement there, made gyratory by the 

 rotation of the earth. 



The friction of one stratum of air gliding over or beside 

 another stratum of air has been found to be infinitesimally 

 small, so that the velocities of two such bodies of air moving 

 from north and south, and meeting about the 35th parallel, 

 would be the final velocities attained by the accelerating force 

 of gravity at this point, and the collision would cause the 

 masses to fall with the momentum produced by the vertical 

 components of their onward and downward motions. 



Is not the high pressure observed in an anti-cyclone due — 

 in part at least — to this downward momentum ? And similarly, 

 is not the low pressure observed in a cyclone due — in part at 

 least — to the upward motion produced primarily by collision 

 of oppositely-flowing currents of air under the influence of 

 gravity, and sustained by the latent heat set free as the vapour 

 of water in the subtropical inflowing current of moist air is 

 condensed by the opposing polar cold current? I suggest 

 the question, but I am unable to assert that the facts are as I 

 suggest. 



I do not think that any good instrument has yet been 

 devised for registering the upward or downward movements of 

 the wind. Such instruments installed at high levels and at low 

 levels would give us, I believe, much valuable information on 

 this very obscure subject. 



As regards the interaction of cyclones and anti-cyclones 

 upon one another in such cases as we observe here, it will be 

 evident that, whatever be the full causes of the high and low 

 barometers in the two systems, they tend to destroy one 

 another, the high filling up the low and the low eating up 

 the high, and both being thus reduced towards the normal 

 pressure. But it is a question of supply and demand. When 

 an anti-cyclone is bordered on both the north and south sides 



