502 W. von Siemens on the General 



that finally the heat produced on the earth's surface, and 

 thereby disturbing the equilibrium, is dispersed through all 

 the overlying air-strata and so restores the indifferent 

 equilibrium of this part of the atmosphere. 



When this heating of the layers of air near to the ground 

 is extended to a whole zone of the earth, the balancing of the 

 indifferent equilibrium disturbed through solar radiation is 

 effected on the same principle, although the resulting phe- 

 nomena are quite different. In this case the upflow would no 

 longer be limited as to space, but comprehend the whole 

 torrid zone systematically, nor can it be limited as to time, 

 but the adjustment, like the cause of the disturbance, must 

 continue unlimited. A continuous system of currents com- 

 prehending the whole atmosphere must consequently be 

 formed, which eventually brings about the continual trans- 

 ference of the extra heat of the air near to the ground in the 

 torrid zone to the whole atmosphere at all levels and latitudes, 

 and restores the indifferent equilibrium disturbed in the torrid 

 zone, through continuous air-currents. 



If the possible lines of currents are constructed, bearing in 

 mind that stream-lines cannot cut one another, that the 

 velocity of an ascending current of air must increase directly 

 as the height and inversely as the pressure, and finally 

 that the air must maintain its velocity unaltered unless ex- 

 pended in friction, mixture, or the work of compression, the 

 system of winds proposed by me is necessarily arrived at, 

 depending essentially on the vis inertia of the heated air set 

 in accelerated motion by the equatorial upflow. This vis 

 inertia not only forces the accelerated rising air along the 

 higher strata of the atmosphere, but is also the cause of its 

 return along the lower strata to the equator. 



It would lead me beyond the scope of this communication 

 were I to enter upon a closer discussion of this vis inertia 

 of the air, and on the influence of the vapour of water, which 

 considerably modifies it. But I may be allowed to say some- 

 thing on the origin of the great stores of local energy 

 indicated by the maximum and minimum pressure of the air. 

 The sum of the pressure of the atmosphere at every part of 

 the earth's surface must be constant, for this sum represents 

 the weight of the invariable total amount of air. A reduction 

 of the pressure of the air at one part must therefore necessarily 

 be always opposed by a simultaneous increase of pressure 

 elsewhere. It is evidently no use to look for the originating 

 cause of the maxima and minima in local conditions of the 

 atmosphere. The barometer frequently gives intimation of 

 these before any alteration takes place in the state of the 



