Optical Phcenomena seen in Switzerland. 



333 



cular spots appear like sparks of the most brilliant white*. 

 Unfortunately all these details, which add so much to the 

 beauty of this splendid phasnomenon, cannot be represented in 



Fig. 1. 



Fig. 2. 



such small sketches. Neither the hour of the day, nor the angle 

 which the object makes with the observer, appears to have any 

 effect ; for on some occasions I have seen the pha?nomenon to 

 take place at a very early hour in the morning. Yesterday it 

 was 10 o'clock a.m., when I saw it as represented in fig. 1. 

 I saw it again on the same day at 5 o'clock p.m., at a different 

 place of the same mountain, for which the sun was just setting. 

 At one time the angle of elevation of the lighted white shrubs 

 above the horizon of the spectator was about 20° ; while at 

 another place it was only 15°. But the extent of the field 

 illuminated is variable, according to the distance at which the 

 spectator is placed from it. When the object behind which 

 the sun is going to rise, or has just b,een setting, is very near, 

 no such effect takes place. In the case represented, fig. 1, the 

 distance was about 194 metres, or 636 English feet, from the 

 spectator, in a direct line; the height above his level being 60 

 metres, or 197 English feet, and the horizontal line drawn fron) 

 him to the horizontal projection of these points on the plane of 

 his horizon being 160 metres, or 525 English feet, as will be 

 seen in the following diagram, fig. 3. In this case only small 



[* This appearance seems to he connected with that assumed by flying 

 birds when seen, under certain circumstances, tiirough a telescope, diu'ing 

 ol)servations on the sun, and wiiich, it has been ailc{;ed, has occasionally 

 been mistaken for that of small meteors sccnjn the day-tiinc: sec the next 

 two pages. — Eurr.] 



