VOL. v.] PHILOSOPHICAL TRANSACTIONS. 46I 



being distant from the sun at a certain angle, on what side soever it be, they 

 begin from thence to give passage to the rays, transmitting them to the eyes 

 of the spectator. And that these halos are probably those we see almost always 

 pass through the two parhelia, that are on the side of the true sun, as the halo 

 G K N I in the phenomenon of Rome. 



That there is yet another situation of these cylinders very considerable, 

 which is so as their axes are parallel to the horizon, but turned divers ways, 

 like needles confusedly thrown on the ground : which horizontal disposition 

 is very natural to those cylindric bodie§, supported by the vapours which rise 

 from the earth, as may be made out experimentally in bodies, thus figured, being 

 let fall in the air. 



That it is in these cylinders that the arches, which touch the halos above or 

 below, are formed ; such as there were in the phenomenon observed at Rome, 

 An. 1630, which is described by P. Schenir in a letter to M. Gassendus, as 

 also in all those which M. Hevelius has related at the end of his Mercurius in 

 Sole. And that the arch which appeared on this last halo at Paris, was of the 

 same kind. That the figure of these arches is different according to the dif- 

 ferent altitudes of the sun, and the several magnitudes of the diameters of the 

 halos. That when the sun is very near the horizon, such an arch appearing 

 on an ordinary halo of 44 degrees, must show like two horns, as in fig. 6, 

 A B, AC: but that the sun rising higher, those horns become lower in pro- 

 portion, and make such arches as are represented in the same figure, where 

 each height of the sun is marked near the arch which it is to make. That the 

 place of the arches where they touch the halos, being more strongly enlighten- 

 ed and coloured than the rest, makes us judge that there are parhelia in those 

 places. 



That the reason why these arches do usually touch a parhelion, was that the 

 same horizontal cylinders, which produce the arch, produce also that parhelion 

 by means of their two round and transparent ends ; in the same manner as has 

 been said of the perpendicular cylinders. And that the parhelion last seen at 

 Paris had been formed in these couchant cylinders. That that was also con- 

 firmed by its being brighter in the superior and inferior part, than any where 

 else ; which necessarily comes to pass in a parhelion caused by cylinders thus 

 disposed ; whereas when produced by the round grains, it must appear every 

 where equally strong. 



That in these same cylinders parallel to the horizon, there is also found the 

 cause of the white cross, observed with the paraselenes or mock moons, by 

 M. Hevelius, and exhibited at the end of his Mercurius in Sole : the perpen^ 

 dicular fillet of that cross, coming from the reflection of the rays of the moon 



