356 Prof. Marcet upon the Variations in the Atmosphere* 



to 14°. 4 of Fahr. on a change of elevation of 50 feet. A ther- 

 mometer placed at the height of two feet above the surface, in- 

 cheating 3° Fahr., and another at the height of 52 feet, indicat- 

 ing at the same moment 17°.4. The mean difference, calculat- 

 ing upon twelve observations made during the period of exces- 

 sive cold, between the temperature of two strata of air separated 

 by an interval of 50 feet, was 10° Fahr. These differences 

 were much less conspicuous during fine weather. 



The comparison between the temperature of the air at tico 

 feet, and sit Jive feet above the surface, perhaps presented still 

 more remarkable results than the preceding, regard being had 

 to their great proximity. The difference, calculating from the 

 mean of nine observations (the surface being then covered with 

 snow), was 4°. 2 in favour of the more elevated station ; this dif- 

 ference, on the 4th of January, increased to 7°.2 Fahr. 



A great number of trees in the neighbourhood of Geneva 

 have suffered this winter from the intensity of the frost. The 

 gardeners have remarked, in many instances, that the lower part 

 of the tree was frozen, whilst the upper branches remained per- 

 fectly uninjured. Localities even have been named where a 

 great number of the trees were found frozen to the height of four 

 or five feet, and remained green above this limit. The facts 

 contained in this memoir of M. Marcet serve to account for 

 these apparent anomalies.* 



* Arago, in his Instructions for the use of the Naturalists of the French 

 Arctic Expedition, at present probably in Spitzbergen, has the following 

 remarks : — The physical causes which concur in rendering the strata of 

 the atmosphere calder in proportion as they are more elevated, have not 

 hitherto been subjected to an accurate appreciation ; on the other hand, we 

 are almost compelled to suppose that there is some essential omission in 

 the enumerations which have appeared. This being the case, it has oc- 

 curred to me that the investigation of an anomaly might better lead to the 

 detection of the deficiencies, if any exist, and furnish the means of supply- 

 ing them, than any general study of the phenomenon. This was the reason 

 why I was solicitous to call the attention of tlie naturalists in La Bonita 

 going to the Arctic Zone, to the exception which the usual law undergoes 

 in serene weather y during the night; upon the then increasing progression 

 which the atmospheric temperatures exhibit from the surface of the earth 

 to a certain limit of elevation, which has not yet been exactly determined. 

 At tlie present time this field of research appears to be enlarged. In cer- 



