130 REPORT—1840. 
about 41° from the sun, but is generally stated * to be too faint 
to be visible. Two observations by Bergmann are the only 
recorded ones I have met with}. Kamtz observed a ternary 
bow amidst the spray of the falls of Schaffhausen f. 
275. We have said that the appearance of supernumerary 
bows indicates the presence of rain-drops below a certain size, 
as well as of considerable uniformity of dimension. It is re- 
markable that Langwith observed, more than a century ago, that 
“this effect depends upon some property which the drops retain 
whilst they are in the upper part of the air, but lose as they 
come lower down and are more mixed with one another.”’ M. 
Arago seems inclined to suppose, on the authority of d’Abbadie 
and the officers of the Venus §, that supernumerary bows are 
raret in equatorial climates than in ours. It should be recol- 
lected, however, that Bouguer saw them in South America with 
an unusual degree of vividness and separation|]._ M. Arago has 
recommended to the Academy of Sciences of Paris the execu- 
tion of a good coloured view of the rainbow, as a guide to ob- 
servers. 
C. Halos§ and Parhelia. 
276. The apparent complication of the phznomena of halos 
and parhelia has given rise to a great deal of vague speculation 
and loose though ingenious theory. Observations of facts have 
been likewise wanting in precision. On these grounds, we 
will endeavour very briefly to discuss that part of the sub- 
ject which seems to have been most successfully dealt with, and 
endeavour to refer the explanations which have been given, to their 
proper authors; for so much has been written on the matter that 
the same thing has been produced as new by various writers at 
different times. 
277. What would first be desirable would be a clear state- 
ment of what is to be considered a complete or normal example 
of the compound display of halos and parhelia. The phno- 
menon seen by Hevelius, at Danzig, 20th of February, 1661**, 
which has generally been considered as a characteristic exam- 
ple, consisted principally of— 
* By Young and Babinet. 
+ Abhandlungen der Schwedischen Academie fiir 1759, p. 234. Quoted by 
Brandes. { Lehrbuch, iii. 160. 
§ Annuaire, 1840, p.305. || Mém. de Paris, 1757, p. 60, quoted by Kamtz. 
§ The halos now spoken of are the great halos of 223° and 46° radius, and 
have no reference to the small halos or coronz with which they are often con- 
founded, but which have a distinct origin. 
** Tt is figured in almost every work on the subject. See Huyghens’s 
Op. Reliqua, ii. 38, and Fraunhofer in Schumacher’s Abhandlungen, Heft iii. 
ere 
