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Prof. Chaveland/s description of Halo s and Parhelia. ISI7 



\}ivaj)or^ or of zc<?, or f^f snow^ suspended in the atmosphere. No 

 one^ however^ has yet been able to point out^ in a very satisfaclo- 

 ry manner, all tliose circumstances, which must concur in the pro- 

 duction of Halos and Parhelia ; or to say why particles of vapor, 

 ice, and snow, which are so freqiientlij suspended in the aimos* 

 pltere, should so seldom produce the phenomena, of which wc 



speak. 



It is not my intention, in this paper, to offer any remarks on 

 the causes of Halos and Parhelia; but merely to recall the atten^ 

 tion of Philosophers to the theory of Huyghens, This theory, 

 the outlines of which were communicated to the Royal Academy 

 of Paris, soon after the year 1667, Dr. Priestly says, "has me 

 with the most favourable and the longest reception 



M. Huyghens supposes the light, in these phenomena, to be re- 

 fracted and reflected by particles of ice and snow, suspended in 

 the atmosphere, and existing iu the form of very minute globes, 

 and also of small cylinders with hemispherical ends. These 

 globes and cylinders have an opaque nucleus at the centre, sur- 

 •roundedby a transparent shell ; and may, perhaps, consist of par- 

 ticles of soft snow, which have once been thawed on the outside 

 by the heat of ihe sun. The position of these cylinders may be 



perpendicular, parallel, or inclined. 



M. Huyghens expressed a wish, that, for the entire confirmation 

 of this hypothesis, some of these small cylinders could be observ- 

 ed to fall to the ground, at the time, when Parhelia ceased to ap- 

 pear. Maraldi, Weidler and others have, in fact, observed, that, 

 when Parhelia disappear, snow sometimes falls in the form of ob- 

 long spicula. Within a short time after the phenomena of this 

 kind, which occurred at Brunswick in March 1815, and April 1818, 

 snow fell very copiously. In the former case, its form was that of 



