220 Notices respecting New Books. 



from the equator towards the poles. Our author has investi- 

 gated the height at which this would happen, under certain 

 circumstances, and calculated the velocity of each current at 

 different elevations. The velocity and direction of these cur- 

 rents may be affected by the partial rarefaction or condensation 

 of any of the columns ; and such change of density will na- 

 turally take place, in consequence of the vicissitudes of the 

 seasons, and the alternations of day and night. 



If the sphere be set in motion, and made to revolve around 

 its polar diameter, as an axis, an apparent modification will 

 take place in the direction of the currents. The lower cur- 

 rent, coming from a point whose velocity of rotation is less 

 than that at which it arrives, will appear to be affected with a 

 motion, in a direction contrary to that of the revolution of the 

 sphere ; while the upper current, being under opposite cir- 

 cumstances, will be apparently affected in an opposite manner. 

 Hence we find, in the equatorial regions of the earth, winds 

 that blow continually from N.E. on the northern side of the 

 equator, and from the S.E. on the southern. In this region, 

 the temperature is subject to little variation, and the general 

 causes that have been described are more powerful than the 

 local action ; but, as slight irregularities of temperature are 

 capable of producing great disturbances, that would act un- 

 equally on the antagonist currents, accuirfulations in some parts, 

 and consequent deficiencies would arise, and cause temporary 

 and variable winds, that in the higher latitudes would modify 

 the regular currents, and often z-everse their courses. 



The atmosphere is not composed entirely of a homogeneous 

 and permanently elastic fluid, but always contains a considera- 

 ble portion of aqueous matter. It has been supposed by some 

 that this is chemically combined with the air ; by others, that 

 it exists there in the form of vapour. The experiments of 

 Dalton have established, conclusively, that the latter is the 

 true theory; and that every given portion of space is capable 

 of containing, at a given temperature, a certain amount of 

 aqueous vapour, whether there be air present, or not. Mr. 

 Daniell proceeds, in the second part of his first essay, to in- 

 vestigate the phaenomena of an atmosphere composed entirely 

 of aqueous vapour; and the third part treats of one composed 

 of permanently elastic and condensable fluids mixed. It would 

 occupy too much space to follow him in this most ingenious 

 and interesting inquiry ; we shall therefore content ourselves 

 with stating, in his own language, the results at which he 

 arrives. 



" The specific gravity and elasticity of the air is but slightly 

 affected by this intermixture of aqueous vapour; so slightly, 



indeed, 



