334' Prof. Necker's Observations on some remarkable 



shrubs, and the lower half of the stem of a tree, are illumina- 

 ted white, and the horizontal extent of this effect is also com- 

 paratively small ; while at other places when I was nearer 

 the edge behind which the sun was going to rise, no such 

 effect took place. But, on the contrary, when I have wit- 



1000 metres, or 3581 Engl. feet. 



S. Apparent place of the sun. T. Tree illuminated white. 



M. Spectator. 



nessed the phaenomenon at a greater distance and at a greater 

 height, as 1 have seen it other times in the same and in other 

 mountains of the Alps, large tracts of Forests and immense 

 spruce firs were illuminated white throughout their whole 

 leno'th, as I have attempted to represent in fig. 2. and the 

 corresponding diagram, fig. 4. Nothing can be finer than 

 these silver-looking spruce forests. At the same time, though 

 at a distance of more than a thousand metres, a vast number 

 of laro-e swallows or swifts [Ci/pscius alpi?ms), who inhabit those 

 hio-h rocks, were seen in the shape of small brilliant stars or 

 sparks moving rapidly in the air. From these facts, it appears 

 to me obvious that the extent of the illuminated spots varies in 

 a direct ratio of their distance ; but at the same time that there 

 must be a constant angular space, corresponding, probably, to 

 the zone, a few minutes of a degree wide, around the sun's disk, 

 which is a limit to the occurrence of the appearance: this 

 would explain how the real extent which it occupies on the 

 earth's surface varies with the relative distance of the spot from 

 the eye of the observer, and accounts also for the phaenome- 

 non being never seen in the low country, where I have often 

 looked for it in vain. Now that you are acquainted with the 

 circumstances of the fact, I have no doubt that you will easily 

 observe it in some part or other of your Scotch hills : it may 



