46l PHILOSOPHICAL TRANSACTIONS. [anNO I67O. 



on the surface of these cyhnders; as the other fillet, parallel to the horizon, 

 is produced by the reflection of the perpendicular cylinders which make the 

 great white circle, of which this fillet is a part. That yet the moon must not 

 be very high above the horizon, so that the couching cylinders may produce 

 this effect. 



That besides the perpendicular cylinders, and those that are parallel to the 

 horizon, there are often a great many which move to and fro in the air in all 

 sorts of positions ; and that those, for the same reason as the round grains, must 

 produce a halo about the sun, and even a more vivid one than that which is 

 caused by the grains, forasmuch as each cylinder sends many more rays to the 

 eye, than each of these little spheres. That the little halo D E F, in the Ro- 

 man phenomenon fig. 5, may very well have been caused by such cylinders. 



As to those mock suns, which sometimes show themselves directly opposite 

 to the true sun, that he could find nothing, neither in the round grains nor in 

 the cylinders, which should make these suns necessarily to meet in the great 

 white circle, parallel to the horizon ; and that if that should be always verified 

 by future observations, the cause of it must be looked for elsewhere. 



That for the generation of these suns, he supposed a number of small 

 cylinders with opaque kernels, like the foregoing; which were carried in the air, 

 neither perpendicularly, nor couching, but inclined to the plane of the horizon 

 at a certain angle, being near half a right one; to which were particularly ap- 

 propriated those cylinders which M. Descartes saw fall from the heavens, hav- 

 ing stars at both ends; as may be seen experimentally by forming cylinders of 

 that fashion which is represented in fig. 7, and letting them descend in the air 

 or in water. That in these cylinders was found not only the cause of the an- 

 thelia made by the intersection of two arches, as in fig. 8, but also that of some 

 other extraordinary arches and rods, that are sometimes observed near the sun, 

 of which notwithstanding there could nothing be as yet affirmed with certainty, 

 for want of exact and faithful observations. 



To make all these different effects of the cylinders manifest to the eye, M. 

 Huygens produced one of glass, a foot long, of the shape of that in fig. 4 ; and 

 for the opaque kernel in the middle, a cylinder of wood, and the ambient space 

 filled with water, instead of transparent ice: which cylinder being exposed to 

 the sun, and the eye put in proper places, there were successively seen all those 

 reflections and refractions above-mentioned. Whence it might be concluded, 

 that a great number of the like cylinders, although very small in comparison to 

 that, being found in the air, and having the several postures that have been sup- 

 posed, all the appearances of the parhelia and their circles must exactly follow. 



