SOCIETY OF PHYSICS AND NATURAL HISTORY OF GENEVA. 301 



of the spectrum. But if it be admitted tbat iu an assemblage of gases 

 each of tbem may act singly, it would follow tbat tbe atmospbere of by- 

 drogeu, by reason of tbe feeble specitic gravity of tbat gas, must ex- 

 tend mucb further than those of the other vapors, and form, consequently, 

 the exterior envelope of the sun. 



§ 2. — ^]\Ieteoeology. 



Professor Gautier read to us an extended notice on the fourth year of 

 the thermometric and pluviometric observations made at the seventy 

 Swiss meteorological stations, and also on some other analogous labors 

 of MM. Wolf, Plantamour, Marguet, Ilirscb, Fretz, &c. This notice, 

 forming a sequel to those which M. Gautier had drawn up on the first 

 three years of observation, has been published in the number of the Ar 

 chives des sciences physiques et natureUes for jS^ovember, ISGS, 



The meteorology of different regions has formed the subject of som'e 

 interesting communications. Protessor Marcet has related to us his im- 

 pressions regarding the climate of Egypt, where he had resided for sev- 

 eral months. He was especially struck, iu ascending the Nile, at the 

 excessive differences which exist between tbe maxima and minima, 

 according to tbe hours of the day. In tbe month of January it was 

 very difficult to support the beat of the sun at 27^, (80° F.,) or even at 

 22°' or 23° (72° or 73° F.) This is referable, doubtless, to tbe extreme 

 dryness of the air. It scarcely ever rains, iu fact, in Upper Egypt and 

 Nubia. The assertion of Herodotus tbat it bad not rained at Thebes 

 since the time of Psammetichus, that is to say during five centuries, 

 is, no doubt, exaggerated, but it is not the less true that rain is 

 extremely rare in those countries. The dragoman of Mr. Marcet had 

 seen raiu fall but once in fifteen or sixteen years. The radiation 

 produces an extreme coldness at the rising of the sun. It appears that 

 at Ismaila, where many plantations have been formed since labor was 

 commenced on the canal of Suez, it rains more frequently thau of old. 

 In higher Egypt and Nubia the sky is almost always clear. M. Mar 

 cet observed clouds, but be believes that it was a misty appearance pro- 

 duced by tbe Kamsin. 



A summary of meteorological observations made at Hayti during five 

 years was communicated to us by Professor Gautier ; the extremes of 

 temperature observed in that space of time were 13°, 5°, and 38°, (56°, 

 41°, and 100° F.) M. Gautier has received the commencement of ob- 

 servations made, at his instance, ou the coast of Labrador by the Mo- 

 ravian missionaries, to whom he had sent thermometers prepared and 

 regulated at Geneva. 



Professor Plantamour recounted to us the anomalies of temperature 

 observed at Geneva during the month of December, 18G8. The mean 

 was 7°.14:, (45° F.;) being C°.14 (43° F.) higher than for the previous 

 forty-three years. During that period there had been but two months 

 of March and a single November iu which the temperature was higher. 

 So high a temj)erature had not been experienced for any month of Feb- 

 ruar}', nor a fortiori of January, but, again, there had been six Aprils 

 in the same series of years which were colder. There fell in December 

 155 millimetres (6 inches) of water, a quautity greater than that of all 

 the years since 182C, with the exception of 1841. According to M. 

 Wolf, of Zurich, the quantity of water collected at several stations of 

 East Switzerland, especially at those of considerable elevation, from the 

 middle of September to the end of October, 1867, exceeded a metre, and 

 cases occurred in which tbe quantity of water falling in the course of 



