ON VARIATIONS IN DIRECTION AND MOTION OP THE AIR. 267 



On reference to the diagrams of the Liverpool horary variations (Plate 

 VI.), it will be observed that the same general character of curves exists as at 

 "Wrottesley, though the amount of air indicated as passing from the various 

 points differs considerably. The amount of east and north-easterly winds re- 

 corded is, however, much less, owing to the observatory being somewhat shel- 

 tered on that side by the town. The peculiar horary variations which at Wrot- 

 tesley are exhibited in the S. and S.W. winds, extend at Liverpool from the 

 S.E. to the W.S.W., the former showing the greatest amount in the morning, 

 the latter in the afternoon. The extension of these variations over so 

 many points of the compass forms one of the most striking differences 

 between the observations taken at this station and those at Wrottesley. 

 ~No doubt the course and valley of the river Mersey lying in a S.E. direc- 

 tion, also the town of Liverpool situated to the N.W., would have a consi- 

 derable influence in deflecting these south and south-westerly currents, and 

 in giving them a more easterly bearing ; though probably there are other 

 causes in action yet to be discovered. 



The west and north-westerly currents show the same peculiarities as to 

 the difference between the amount of motion in the day and night as at 

 Wrottesley, and at this station exceed that of any other wind. 



The integrating registers for Birmingham having been taken for only 

 three years and a half, have not been engraved; they present much the 

 same features in their horary variations as the observations taken at Wrot- 

 tesley, the only difference worth mentioning being in the great S.W. or 

 anti-trade-current, which has a rather more westerly bearing at Bir- 

 mingham than at Wrottesley. 



The curves that have been obtained by projecting these integrating re- 

 cords of horary variations, especially those of the south and south-westerly 

 winds, differ much from those of force or velocity as given by me in former 

 papers to this Association, when it was shown that the latter nearly 

 coincide with the curves of temperature, the greatest force occurring at or 

 shortly after noon ; but by subjecting the present observations to the test of 

 velocity by dividing the number of miles of air that pass during each hour 

 of the day throughout the year, by the number of hours occupied in passing 

 (see Table II.) it will be found that the law as. to the period of greatest 

 force or velocity is still correct, notwithstanding that some of the curves 

 show a larger amount in other parts of the day. These curves are there- 

 fore interesting and important, as showing that the different currents have 

 forces acting on them producing horary variations, besides those of acce- 

 leration from increase of temperature. In the last row of diagrams. Plates 

 V. and VI., curves are projected on an enlarged scale, showing the horary 

 variations in the velocity of the air at Wrottesley and Liverpool. 



The next series of observations have reference to the amount and direction 

 of the various winds throughout the year. In tabulating these, it was neces- 

 sary that each day should be recorded separately, for by throwing together 

 an arbitrary term of days, as a month or even a week, many important facts 

 would be lost. The records have therefore been tabulated so as to give the 

 direction, duration, and amount of horizontal motion of the air for every day 

 in the year for seven years, referred to sixteen points of the compass. Com- 

 mencing with the 1st of January in each year, the number of hours that 

 each current has lasted, and its amount of horizontal motion during the day, 

 are obtained from the diaries in which the indications registered by the instru- 

 ments are recorded, and this is repeated in rotation for every day during seven 



