state of the Atmosphere for the Science of Meteorology . 45 



observations, that MT therefore could be considered as the 

 equilibrial state of temperature at a determined season of the 

 year at that place; then we should find that the differences 

 OT — MT, ot— mtnre to be ascribed to these circumstances : — 

 1st, that the winds had not in that space of time the same 

 direction as usual: and 2nd, that the distribution of tempe- 

 rature at the surrounding places was quite different from the 

 usual distribution during that space of time, or shortly before. 

 Thus it is necessary that we know the variations, not only for 

 the place itself for which we desire to explain the temperature, 

 but also for the surrounding places, since the variations at the 

 first place must be explained partly from the variations at the 

 latter. The most important causes are always to be sought 

 in the variations (deviations); it is from those that we must 

 derive the exhibition of the state of temperature, not from the 

 absolute observed temperature. Even now, when we give 

 absolute temperatures, we do in fact give deviations ; namely, 

 deviations from the arbitrary zero of temperature. Positive 

 prognostications will always be given under the form of de- 

 viations, and best by deviations from the mean state of the 

 atmosphere. Certainly it were to be wished that we better 

 understood the theoretical temperature (©), which must take 

 place for certain soils and elevations above the sea, and for 

 every latitude, in order also to be able to give the deviations 

 from those theoretical values; but for want of that knowledge 

 the deviations from the mean value are the main points for con- 

 sideration. 



Art. III. Temperature is that state which most attracts 

 the attention of the public, in consequence of the immediate 

 influence it has on the relations of human life; but scientifi- 

 cally, all states are equally important. The pressure of vapour 

 is perhaps the most uncertain element, and of which we can 

 give little explanation, from the manner in which it is mea- 

 sured ; electricity is not anywhere (with exception of Brussels 

 and Kew) sufficiently known either as to its origin or as to its 

 quantity; it is not therefore expected that the deviations of 

 these elements can be given. It is the winds that bring us the 

 warm air and cold waves ; they must be accurately noted as to 

 direction and^strength, but it will avail little to give their devia- 

 tions from the mean direction ; the winds must therefore be 

 noted with their real directions. On the contrary, as to the 

 barometer, the deviations again are of the greatest importance, 

 especially as here the theoretical state is known for every lati- 

 tude. Everywhere, where attention has been paid to the de- 

 viations of the barometer, which at the same time have been 

 observed at different places or successively at the same place, 



