504 SCIENTIFIC RECORD FOR 1883. 



tinguished from that of the clouds, the earth, and the apparatus, it 

 would seem best for the meteorologist to await the studies of the 

 physicists and refrain from advancing crude explanations. Observa- 

 tions and inductions are always in order; working hypotheses are very 

 helpful as suggesting further observations and study, but they should 

 not be put forward as satisfactory explanations. Perhaps the most 

 important new contribution in this essay is Buchan's new charts, based 

 on the eleven years, 1870 to 1880, and giving the January and July 

 isotherms, isobars, and winds; these must immediately replace his older 

 ones of 1868, and even those of Ferrel, Met. Kes., Part I, (1877,) after ap- 

 plying the reduction of barometer to standard gravity, which has been 

 omitted by Buchan. 



In his comments on these charts our author seems not to clearly 

 state the mechanical problem of the connection between isobars and 

 winds; he says, "Winds set in from where there is a surplus to where 

 there is a depression of air, and observations teach that the isobars and 

 the prevailing winds are in accordance with each other," and in his sub- 

 sequent detailed exposition of these accordances the fact seems to be 

 lost sight of that our winds are primarily due to differences of temper- 

 ature and moisture as affecting density, and that from the winds and 

 the rotation of the earth follows the distribution of pressure, as shown 

 on his valuable maps, whose isobars are, therefore, the result, not the 

 cause, of the winds. 



Thisdynamicphenomenon, so ably exposed by Ferrel, Babinet, Everett, 

 Hann, Finger, Sprung, Thiesen, Both, Overbeck, Guldberg, and others, 

 will, we hope, ere long be accepted by English meteorologists. In such 

 sentences as, "differences of pressure and consequently all winds, origi- 

 nate in changes of temperature, &c.,"or, "all winds may be regarded as 

 caused directly by differences of pressure," Buchan alludes to differ- 

 ences measurable by the barometer as is generally the case in storms, 

 and known as barometric gradients, whereas these gradients are tbe 

 result and not the cause of the wind, the true cause being the very slight 

 gradients of pressure due to differences of density ; these fundamental 

 gradients are very slight, and in the exact direction of the wind, while 

 the resulting ordinary barometric gradient is measured perpendicular 

 to the isobars, and therefore frequently at a considerable angle to the 

 wind. 



It is impossible for one familiar with recent advances in dynamic mete- 

 orology to accept the explanation that Buchan offers of the cause of the 

 general low pressure over the sea in winter and the land in summer, 

 and perpetually at the equator and poles, based on the simple principle 

 that moist air is lighter and that the condensation of moisture leaves a 

 perceptible vacuum. "Air charged with vapor is specifically lighter than 

 when without the vapor ; the condensation of vapor in ascending air is 

 the chief cause of the cooling effect, being somewhat less than that which 



