406 



Mr. F. Chambers on the Variations 



[Dec. 7, 



where 



M = < - ^ ^ ^- 1 15° X 69-16 X cos 



KJN' +N' \ 

 ^-i j X 15° X 69-16 X cos & 



> .... (2) 



'W +N' 



and 



-E 



E + E' E + E' 



M.^ =< \ t - — X (0-0') X 69-16 ... (3) 



in which is the north component of the wind variation for the hour h 

 and the parallel of latitude 0, and N'^ the corresponding north component 

 for the parallel of latitude d' , E^ the east component of the wind variation 

 for the hour h and the parallel of latitude 0, and E'^^ the corresponding 

 east component for the parallel of latitude 0'. 



Suppose, then, the existence of twenty-four blockades formed by the 

 twenty-four meridian Hues corresponding to the twenty-four full hours, 

 and by the equator and the parallel of north latitude, taken as 32° 23', 

 on which Bermuda stands. Bearing carefully in mind that only the 

 diurnal variations of the wind are being considered, the mean diurnal 

 variation of the north component of the wind for the whole year at Ber- 

 muda affords the means of calculating how much air flows into or out of 

 each of these blockades on the north, and the corresponding variation of 

 the east component of the mnd affords the means of calculating the 

 quantity of air which flows into or out of them on both their east and 

 west boundaries, i, e. across each of the meridian- hour lines, on the 

 supposition that the variation of the east component of the wind is the 

 same between Bermuda and the equator as at Bermuda, an assumption 

 which is doubtless only approximately true, and though somewhat rough, 

 yet sufficiently exact for our present purpose. But we have no observa- 

 tions to show how much air flows across the equator into or out of each 

 of them. To tentatively supply the place of such observations the mos.t 

 simple supposition that can be made is, that there is no transfer of air 

 across the equator either into or out of any of them, or, in other words, 

 that on the equator there is no diurnal variation of the north component 

 of the wind. It seems probable that this assumption is not strictly true, 

 but that the position of the line at which the outward currents from the 

 neighbourhood of the equator may be said to originate, or at which the 

 return inward currents may be said to meet, not only has an annual 

 variation about its mean position, but that it also varies from hour to 

 hour, or, in other words, that there is no single line which satisfies the 

 assumption made for all the hours of the day. But, for our present pur- 

 pose, the assumption that the equator does so will probably not very 

 essentially affect the results arrived at. 



