278 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



the isothermal surface of o° C. or to consider it as the carrier of the 

 positive electricity, when there is nothing else present in this layer 

 except atmospheric air and gaseous matter and no condensed aque- 

 ous vapor. 



I could indeed imagine that the cirrus clouds are the carriers of the 

 positive electricity, but since these clouds are wholly absent on 

 many clear days while on others they float at very great altitudes, 

 therefore this assumption would not suffice to explain the diurnal 

 and annual periods in atmospheric electricity, whose cause Sohnke 

 thinks he has found in the oscillations of the altitude of the iso- 

 thermal surface of o° C. 



Moreover, if this surface possesses any such importance then its 

 entrance into the earth, that is to say, the fall of the air temperature 

 at the earth's surface below the freezing point, must cause a con- 

 siderable diminution of the potential gradient, if indeed it does not 

 cause a complete reversal, whereas, on the other hand it is precisely 

 during very cold and dry winter weather that this potential gradient 

 has especially high values. 



But these are questions that really do not belong here. If I 

 have discussed them, I have done it for fear lest any one should 

 imagine in the views that I have presented a new support for a 

 theory that, in my opinion, has found too ready acceptance by 

 many meteorologists and which we ought to view with critical eye, 

 although I do not deny that it has some value and is worthy of 

 closer study. 



The expositions contained in the preceding memoir may be 

 summarized in the following theorems: 



(1) If supersaturated vapor or subcooled water is present in the 

 atmosphere then the sudden dissipation of such a condition must 

 produce a quick variation of pressure that must make itself visible 

 by a rapid rise and subsequent fall in the barometer. 



(2) If cooling precipitations fall quickly after this dissipation 

 then the barometric fall will be diminished or even entirely pre- 

 vented and a jump in pressure or "step up" rather than an oscilla- 

 tion, will take place by reason of the contraction of the surfaces of 

 equal pressure due to the cooling and the consequent inflow of air 

 from above. 32 



a2 On the theory of the origin of barometric jumps compare the following 

 memoirs by Dr. Max Margules: Vergleichung der Barogramme, etc. Met. 

 Zeit., XIV, 1897, pp. 241-253. Einige Barogramme und Thermogramme, 

 etc. Met. Zeit., XV, 1898, p. 1-16. (Note added in 1905. W. v B.) 



