306 



wind, within the storm itself. Any observations I have had the opportunity of 

 making are totally inadequate to determine any of these elements, and can 

 only leave the subject in the hope that others having better opportunities will 

 work it up. 



Art. LYII. — On Periodic Vertical Oscillations in the Eartlis Atmosphere, and 

 the Connection existing hetiveen the Fluctuations of Pressure, as indicated 

 hy the Barometer, and Changes in the Weather. By H. Skey, Government 

 Meteorological Observer at Dunedin. 



{Read before the Otago Institute, August 9, 1870.] 



That vast commotions take place in this aerial ocean, at the bottom of which 

 we live, is proved not only by the fluctuations of the barometer, but by every 

 gale that blows ; and the study of those laws which have been given to nature, 

 by which all the meteorological phenomena we perceive ar-e effected, is 

 engaging the attention of many. Many kindred sciences meet in atmosphei-ic 

 investigations, but it is proposed, on this occasion, to consider only some of 

 the mechanical, thermal, and chemical laws which influence the weather. 



Great differences in the amount of solar heat received by the earth occur 

 at different latitudes, and also in different degrees at the same latitudes, arising 

 from the varying power of the air to transmit heat ; and it has been shown by 

 Tyndall that though air laden with aqueous vapour may retain its trans- 

 parency to light, yet the heat rays are nearly all checked in their transmission, 

 being absoi"bed by the watery vapour. 



When, therefore, masses of air are thus difi'erently heated, the more heated 

 portion expanding, ascends, and denser air rushes under to restore equilibrium. 

 But the motion imparted to the atmosphere does not end here. If we suspend 

 a weight by an elastic string, we shall be enabled in some measure to illustrate 

 the effect of motion imparted to elastic substances. Mark, flrst, the position of 

 the weight while free ; this will indicate mean pressure and equilibrium. If it 

 is now pulled down, the maximum pressure will be shown ; and when relieved 

 of the maximum pressure, the weight not only goes back to the mean, but 

 nearly as far above as it was pulled down below it, and will continue to vibrate 

 vertically until brought to rest by friction. Observe, also, how regular is the 

 time of vibration. In such a highly elastic medium as the earth's atmosphere, 

 any portion of it being compressed and then relieved from pressure will expand 

 in virtue of its elasticity ; and from its inertia, as expressed in the first 

 IS^ewtonian " law of motion," will continue its expansion until it exceeds its 

 original volume, after which it will again contract, and thus oscillate on 

 alternate sides of its mean volume. 'Now, when any large mass of the air is 

 raised above the mean height of the atmosphere, the direction of the main 



