142 Unufual Appearances by ierrejlrial RefraSlhn. 



will not alter the pofition of their parts, in rcfpe£l to the horizon ; that is, the image of the 

 highcft partof the obje£t will be uppermoft, and the i:Tiage of the loweft part will be under- 

 moft. The figures, however, of the fun and moon, when near the horizon, will fufFer a 

 change in confequence of the refradlion of the under limb being greater than that of the 

 upper, from which they affume an eliptical form ; the minor axis of which is perpendicular " 

 to the horizon, and the major axis parallel to it. But a perpendicular objed:, fituated upon 

 the furface of the earth, will not have its length altered by refraftion ; the refraiSion of the 

 bottom being the fame as that of the top*. Thefe are the efFefts which are produced upon 

 bodies at, or near, the horizon, in the common ftate of the atmofphcre, by what I fhall call 

 the tiftial refraftion. 



But befides the ufual refraiiSlion which afFe£ls the rays of light, the atmofphere over the fea is' 

 fometimes found to be in a ftate which rcfradts the rays in fuch a manner, as to produce other 

 images of the objeiSl, which we will call an effect from an unufual refradtion. In the Phil, 

 Tranf. for ijg--, Mr. Huddart has defcribed fome efFeiS? of this kind, which he has accounted 

 for, by fuppofing, that from the evaporation of the water, the refradive power of the air is not 

 greateft at the furface of the fea, but at fome diftance above it; and this will folve in a very 

 Ikuisfactory manner, all the phenomena which he has obferved : but effects very different from 

 thofe defcribed by Mr. Huddart, are fometimes found to take place. Thefe I had an oppor- 

 tunity of obferving at Ramfgate, laft Summer, on Auguft the firft, from about half an hour 

 after four o'clock in the afternoon, till between feven and eight. The day had been extremely 

 hot, and the evening was very fultry; the fky was clear, with a very few flying clouds. I 

 Ihall defcribe the phenomena as I obferved them with a terreftrial telefcope, which magni- 

 fied between thirty and forty times ; they were vifible, however, to the naked eye. The 

 height of the eye above the furface of the water, at which raofl of the obfervations were made, 

 was about twenty-five feet; fome of them, however, were made at about eighty feet from the 

 furface ; and it did not appear that any of the phenomena were altered, from varying the height 

 of the eye, the general efFedt remaining the fame. 



The firft unufual appearance which I obferved, was that which is reprefented in Plate VII. 

 fig. I. Direfting my telefcope at random, to examine any objedts which might happen to 

 betn \\tvr, I faw the top of the mafts of a fhip. A, above the horizon, x y, of the fea, as (hewn 

 in the figure. At the fame time alfo, I difcovered in the field of view two complete images, 

 B, C, of the fln'p in the air, vertical to the fliip itfelf. B being inverted, and C ereifl, having 

 their hulks joined. The phenomenon was fo ftrange, that I requefteda perfon prefent to look into 

 the telefcope, and examine what was to be feen in it, who immediately defcribed the two 

 images as obferved by myfelf ; indeed they were fo perfedt, that it was impoflible we could 

 differ in our defcription. Upon this, I immediately took a drawing of the relative magnitudes, 

 and diftances of the fhip, and its images, which at that time were as reprefented in the figure, 

 as near as it was pofFible for the eye to judge ; and it was very eafy to eftimate them to a very 

 conftdeiable degree of accuracy. As the fliip was receding from the fhore, lefs and lefs of its 



* See my Complete Syftem of Aftconomy, art. 194. 



mafts 



