TRANSACTIONS OF THE SECTIONS. 3S 



and afterwards veer round by W. with great violence to N.W. or N. The advocates 

 of the rotatory hypothesis find a solution of this by supposing that at those places 

 where the wind veers from S.W. by W. to N.W., a vast body of air is in a state of 

 gyration from right to left, and in a state of translation from S.W. to N.E. 

 TTie centre of rotation is supposed to lie far to the north of the stations where 

 the wind goes through these points. This is a very plausible explanation of 

 the veerings, and is always adduced in support of the rotatory hypothesis, in 

 favour of which much may be said in one class of storms, but in these there 

 can be no rotation, as the S.W. wind flows in one broad stream over the island, 

 and no observations can be found to indicate a recurring of the S.W. wind. 

 In the class of storms where the wind goes through the course of S.W., W . 

 to N.W., an upper current from the N.W. prevails. The veering, Mr. Russell is 

 of opinion, may be accounted for in the same way as variations in the summer 

 months, which arise, he thinks, from an intermixture and interchange which is 

 effected along the course of the wind, the hot air rising up and the cold air de- 

 scending. A similar phenomenon is to be seen in the commingling of water. 

 This, too, he believed, affords a proximate explanation of many of our easterly gales ; 

 and so the reversal of the lower current by the heat of the sun during certain states 

 of our atmosphere in summer is maintained bj' the constant ascent and descent of 

 the air of the two opposite currents, so far as the south wind extends. Every gust 

 of the breeze must be considered as the effect of vertical gyrations caused by air of 

 different specific gravities. As soon as the sun lessens his heat, the disturbing 

 influences are diminished, and at last night brings a calm at the earth's surface, 

 while the north current above still flows on. The length of time which the wind will 

 blow from the S.W. is very uncertain. It commonly varies from eight to forty- 

 eight hours, and in some cases it continues for days. The wind at once turns round 

 to the N.W., when the barometer again begins to rise. The cause of this change of 

 •wind to the N.W., he believed, is merely the upper current resuming its sway at the 

 surface of the earth by putting the thin stratum of air which has been flowing from 

 the S.W. into the same course as the current above. The temporary eruption 

 of the S.W. wind, which has been heated over the warm ocean and replenished by 

 moisture, appeared to him to be a parallel phaenomenon to the southerly breezes 

 which play over our island during the day in summer when the N. wind is prevailing 

 above. These dry breezes are daily called into action by the solar rays disturbing 

 the equilibrium of the air in the lower depths of the atmosphere where rarefaction 

 takes place. In this manner, then, may the moist S.W. winds from the Atlantic be 

 hurried over the continent of Europe, and when once set in motion they possess a 

 self-sustaining force in mingling with the dry cold current which overstratifies them. 

 Although it may be against general theory and beUef, he thought that the returning 

 polar current in our latitude is much more frequently from the N.W. than from the 

 N.E. Both Mr. Green and Mr. Mason were of opinion, from their aeronautic 

 experience, that in whatever direction the wind might blow at the surface of the 

 earth, at 10,000 feet the current was invariably from some point between N. and W. 

 This opinion was no doubt carried too far, but it clearly showed the frequency of 

 the N.W. wind above the lower currents. Many of the storms which begin to 

 blow from the S.W. and veer round to N.W., are apparently caused by the mutual 

 action of two currents from these quarters stratified over one another. In these 

 storms, too, the bEirometer does not usually give much warning of their approach ; 

 indeed the mercury will sometimes be actually on the rise when cirrostratus cloud, 

 the precursor of the S.W. wind, is already formed along the western horizon. On 

 the contrary, the storms which come on with easterly winds give notice of their 

 approach by a fall in the mercury. In conclusion, Mr. Russell observed that the 

 extraordinary change of the wind from S.W. to N.W. had been noticed by Shak- 

 speare, and he had some very beautiful lines on the subject, which Mr. Russell 

 quoted. 



On Parhelia observed at St. Ives. By 3. K. Watts, F.R.G.S. 



These beautiful phaenomena were «een on Tuesday, the 15th of February, 1853, 

 from about IS*" 20"° p.m. to 2'' 30"" p.m. The wind at the time was north-west, 

 very slight; barometer, 29'65 ; thermometer, 31°. The morning was clear, with a 



1853. 3 



