SOCIETY OF PHYSICS AND NATURAL HISTORY OF GENEVA. 303 



are alwavs killed, and one or t>ro furrows may be traced descending- from 

 the summit to the soil. To the right and left of the furrow are seen 

 two strips of alburnum deprived of bark, the width of which increases 

 as they approach the ground. The effects of the lightning which fell, 

 on the 17th of July, on a fir tree in the city of Nyon were very remark- 

 able. The stroke was preceded by the appearance of a luminous ball 

 which moved along the surface of the ground at thrqe or four yards 

 from the tree, an electric phenomenon often described by physicists and 

 in particular by Arago. The fir was about 10.50 metres (51 feet) in 

 height. In its upper part the leaves were scorched to the half of their 

 length. The trunk showed no injury in its upper half, but below there 

 were several very deep fissures and ten or twelve brownish and circular 

 spots from 3 to 5 centimetres (1 to 2 inches) broad, where the baric had 

 been removed. The vine struck, in July, 1808, presented a regular circle 

 of 14 to 15 metres, (15 to 50 feet,) comprising about three hundred and 

 fifty stems, on which nearly all the leaves were mottled with reddish 

 and olive-colored spots. The intensity of this coloration increased on 

 approaching the center. The props were neither burned nor broken. 

 Dr. Miiller, who examined the branches and leaves of the vine-stocks 

 reached by the lightning, found that there was no modification of the 

 cellules in the interior, and that the effect had taken place on the nitro- 

 genized matter, and especially on the cambium. 



The memoir of M. Colladou was accompanied with designs, samples, 

 and strips of the bark, which greatly contributed to the understanding 

 of the effects of lightning on'the trees. Professor j)e La Eive cited 

 some observations in confirmation of those of M. Colladon. He thinks 

 that the spots observed are analogous to those of every electric dis- 

 charge, and which are also circular. Their appearance would seem 

 referable to the presence on the trunk of some foreign substance. 



Professor De La Eive communicated to us the result of the observa- 

 tions of ]M. Wild on the absorbent power of light by atmospheric air, 

 and gave us the analysis of the most recent investigations of jM. Becque- 

 rel and M. Tyndall on the physical and chemical phenomena of light. 

 He called our attention to the observations which have been made at 

 the observatory of Greenwich on the agreement of magnetic and galvauo- 

 metric curves. These curves are nearly identical, the only difference 

 being the following : A point of a curve of the galvanometer always pre- 

 cedes the corresponding point of the curve of the magnetometer. 



M. Ed. Sarasin couimunicated the result of his researches on the 

 phosphorescence of rarefied gases after the passage of the electric spark, 

 and particularly on the part borne by oxygen in these phenomena, 

 (ArcJdres, March, 1809.) 



Professor Marignac detailed his experiments on the heat of the vola- 

 tilization of ammoniacal salts. He has arrived, by prolonged and minute 

 researches, at the conclusion that it is exceedingly probable that the 

 salts of ammonium are, in great part, decomposed into their elements 

 when volatilized, [Archives, November, 1808.) 



Professor Wartmann, besides several reports on the memoirs pub- 

 lished by other savants, gave an account of two luminous phenomena 

 which he had had an opportunity of observing : First, a magnificent 

 solar spectrum on the surface of the lake, seen on the road from Her- 

 mance, a phenomenon which could only be explained by a refraction fol- 

 lowed by a reflection of the solar rays' by the waves ; secondly, a lumi- 

 nous vertical column after the setting of the sun. This meteor, of which 

 he published a notice in 1810, is susceptible of explanation by vertical 

 prisms of ice held in suspension in the atmosphere. 



