454 Dr. Werner Siemens on the Conservation 



the torrid zone which form an expanded ring of air above it, 

 which must flow over towards the poles, and he accounts for 

 the constant change in direction and strength of the winds 

 by the conflict between this equatorial current and the masses 

 of air returning from the poles towards the equator. Even 

 if there were no true ground to be found for this contest of 

 opposed currents of air, and although it was not easy to 

 understand why, with the great uniformity of the mean pres- 

 sure of the whole atmosphere, the air should move with such 

 great energy from the polar regions towards the equator, so 

 distant in comparison with the height of the atmosphere, yet 

 his explanation was at any rate more satisfactory than the 

 usual almost exclusive reference of the motions in the at- 

 mosphere in high latitudes to maxima and minima of atmo- 

 spheric pressure, of which one is absolutely unable to say 

 whence they come and whither they go. These explanations 

 of the direction and strength of winds can be regarded as 

 having a scientific foundation only when it is shown where 

 the forces act and are located which accumulate such enormous 

 energy in maxima and minima, in a maimer often not at all 

 evident, and which then, in turn, produce storms and 

 cyclones. 



An attempt is made in the following pages to supply these 

 gaps from the Theory of the Conservation of Energy. 



It is universally admitted that all life and all motion on 

 the earth originates in the sun's radiation. Without a supply 

 of heat from the solar radiations the atmosphere would be 

 without motion, or rather would follow the earth's rotation 

 without any proper relative change of place and temperature, 

 if we neglect the radiation of the stars and the earth's in- 

 ternal heat. The rotation of the earth would give to the 

 atmosphere the form of an ellipsoid of revolution, assuming 

 that at the temperature of space it was still gaseous and 

 obeyed Mariotte's law, but could not produce any permanent 

 circulation of air. Since the mean temperature and mean 

 motion of the atmosphere change in any definite time just as 

 little as the rotation of the earth itself, there must be stored 

 up in the earth's atmosphere a constant quantity of solar 

 energy in the form of sensible and latent heat, potential 

 energy of masses of air in motion or local accumulations of 

 pressure. Consequently the supply of heat from the radiation 

 of the sun and stars must be equal to the loss of heat by 

 radiation into space. The supply of heat is effected partly by 

 the direct absorption by the atmosphere of the rays which 

 traverse it, but chiefly by the heating of the earth's surface, 

 and the heat thus absorbed is chiefly used up in warming the 



