Optical PJia^nomcna seen in Switzerland. 3">\ 



of the sky situated to the west and north-west were hazy, and 

 with some Httle clouds ; while tlie eastern and southern parts 

 were perfectly pure and clear, and the chain of the Alps quite 

 pure and bright. 



The very rough and inaccurate sketch is a copy of the one 

 which I made rapidly at the time, to preserve the memory of 

 the fact. I well know that the halos and arches must be por- 

 tions of perfect circles, and parallel to each other; but it be- 

 ing easy to make this correction in the mind, 1 preferred 

 giving the thing as I sketched it in haste two years ago. 



I am happy now to be able to give accurate information 

 about the state of the atmosphere in the day itself of the 

 phaenomenon, and in the days preceding it, by referring to the 

 meteorological tables of the Bibliotheque Universelle, to which 

 you may look for more particular details. I see that on the '24th 

 of May 1830, the thermometer of Reaumur had stood be- 

 tween 10° minimum and 20°*8 maximum; then came rain; 

 and by my notes I see that snow fell on the 25th on the Jura, 

 which was melted on the 26th. On the St.Bernard (1278 toises 

 above the level of the sea), the 24th of May, the temperature 

 was between +2° R. minimum, and +8° R. maximum, when 

 rain fell, and the thermometer on the 25th of May descended 

 to — 0°"2 R. minimum, and +4°*5 R. maximum. On the 27th 

 and 28th of May, snow fell on the St. Bernai'd, and the tem- 

 perature decreased till the 29th of May, when it was so low 

 as to reach — 6°'l R. minimum, and +4°'5 maximum. On 

 the 30th of May it had risen again to — 4°*8 R. minimum, 

 and -f-5°*4 maximum; and on the 31st to — l°'l minimum, 

 and +5°*7 maximum : so much for the temperature of the 

 high parts of the atmosphere at the St. Bernard. During the 

 same time, in the lowland at Geneva, since the rain of the 

 25th of May, the thermometer had gradually lowered till the 

 30th of May, when it had attained + 3°*2 R. minimum, and 

 + 15°*4 R. maximum. On the 31st of May it had already 

 risen to +10° R. minimum, and +14'°'4 R. maximum. 



Now on the 1st of June 1830, the day of the parhelia, the 

 thermometer at Geneva was between +3°*5 R. minimum, and 

 + 17°'3 R. maximum. The last must have been nearly the tem- 

 perature during the phaenomenon in the plain. At the St. 

 liernaid on the same day, the thermometer was between — 3°'6 

 R. minimum and +9° R. maximum. This last temperature 

 may give an idea of that of the atmospheric strata at lOOOtoises 

 above Geneva, at tlie time of the parhelia. The whole day 

 was serene and cloudless at the St. Bernard. At Geneva it 

 was likewise so, except in the afternoon, when a thin mist or 

 liazc, and some light clouds, appeared in the west. 

 2 U 2 



