THE SUN AND SOLAR PHENOMENA. 



53 



coronas and halos parhelia have often appeared, and are very common in high latitudes. 

 They are images of the real luminary supposed to be formed by reflection from a cloud. 

 A description of one occurs in the Philosophical Transactions for 1733, as witnessed by 

 Whiston: " About ten o'clock in the morning, Oct. 22d. 1721, being at the house of 

 Samuel Barker, Esq., of Lyndon, in the county of Rutland, after an Aurora Borealis the 

 night before, wind W.S.W., I saw an attempt towards two mock suns. About half or 

 three quarters of an hour after I found the appearance complete, when two plain parhelia 

 or mock suns appeared tolerably bright and distinct, and that in the usual places, namely, 



in the two intersections of a 

 strong and large portion of a 

 halo. The mock suns were evi- 

 dently red towards the sun, but 

 pale or whitish at the opposite 

 sides, as was the halo also. Look- 

 ing upward we saw an arc of a 

 curiously inverted rainbow. This 

 arc was as distinct in its colours 

 as the common rainbow, and of 

 the same breadth." 



The above appearance was re- 

 peated several successive days, 

 and continued each day about 

 two hours. " October the 26th, 

 about nine in the morning, as I 

 was coming in the Northampton 

 coach towards London, the halo 

 returned larger and clearer than 

 before, and the mock suns just 

 attempted an appearance as on 

 Sunday ; but, the air becoming 

 thicker and thicker towards rain, 

 I saw no more." 



The apparent diameter of the 

 sun varies at different seasons of 

 the year; it is least about the 

 end of June, and greatest about 

 the end of December. The dif- 

 ference between the two amounts to about one minute of a degree. There would be 

 obviously no variation, if the orbit of the earth was a perfect circle^ with the sun situated 

 in the centre, for then our distance from him being always the same, his appearance to us 

 would be invariable. But his apparent diameter increases and diminishes, because the 

 ellipse which the earth describes alternately increases and diminishes our proximity to him. 

 When we are most remote, he of course appears least, and is said to be in apogee, a word 

 compounded of awo yr/e, signifying away from the earth ; when we are nearest, he appears 

 greatest, and is said to be in perigee, from Trtpi yi?c, near the earth. It seems extraordinary 

 at first sight, that at mid-winter, when the streams are ice-bound, the snow lies upon the 

 fields, and the traveller shivers in the blast, we should be nearer to the sun than when, 

 at an opposite season of the year, the greensward is burnt up, the cattle pant in the shade 

 of the trees, and men seek a covert from the solar heat. But the effect of the sun's rays 

 is increased or modified by two circumstances, more than sufficient to counterbalance that 



Parhelion 



