538 On the Lines of equal Barometric Pressure. [Feb. 1^ 



have here at once an explanation of tlie difference of directions found 

 by me, and a proof of the conservation of the excess (or defect if pro- 

 ceeding towards the equator) of the initial latitude velocitj ; that is to 

 say, another proof of the earth's rotation. 



It is obvious that this explanation refers only to the mass of air set in 

 motion by the same cause ; it is probable, however, that the lower and 

 upper strata are frequently propelled in different directions. This is evi- 

 dent in the case already noticed of the north-east winds and cirrus currents 

 (footnote, p. 531) ; and is shown without doubt in the cases for which 

 the upper currents proceed from points negative of the lower currents. I 

 may also remark that the difference of direction of these currents will 

 depend on the nature of the surface and on the difference of latitudes 

 of the place from which the air originally started and the place over 

 which it is moving. It is probably due to this cause that the difference 

 — is found greatest for winds from the southern quadrants; but this 

 difference and its relation to 6 v^ ill be considered in a special investigation. 



It is not my intention at present to enter into the many consequences 

 which follow from the facts developed in this paper. It is evident that 

 they indicate a wholly new theory of the circulation of the atmosphere. 

 It was believed that the air was continually flowing into atmospheric 

 basins ; and as the barometer gave no indication of the fact, it became a 

 logical necessity, as the air could not flow out below, that it must rush up 

 above and flow off in still more rapid currents in directions for which 

 there was neither law nor reason. It appears that the air does not pour 

 into these basins, but that it moves as a whole in the directions of equal 

 pressure. 



Fostscriptum. — I have remarked (see footnote, p. 526), on Mr. Buchan's 

 authority, that Dr. Buys-Ballot had found the direction of the wind 

 relativ ely to that of the isobars to be between 10° and 30°, giving an aye- 

 rage of 20°. Mr. Buchan informs me (in a letter dated Dec. 27, 1876) 

 that this result was communicated to him by letter. I owe also, at the 

 same tiuie, to the eminent Scottish meteorologist the communication of a 

 similar investigation by the Eev. "W. Clement Ley, some of wliose results 

 I am glad to be able to add to this paper. 



Mr. Clement Ley has projected the isobarics obtained from the 

 observations for one hour made at 15 stations, telegTaphed daily : by means 

 of a graduated circle he obtained approximately the directions of the 

 isobars at each place (for three months nearly). These directions were 

 then compared with the telegraphed wind directions, which were given to 

 two points of the compass only ; he found the average inclination of the 

 wind to the isobar (d — (pj to vary at the different places from +5° to 

 -1-41°, and that the mean of the whole gave 



e—ip=-\-21° nearly. 



Consideriog the many sources of error in the telegraphed observations, 



