Hennessy — On Teminrature over Great Britain, 8fc. 711 



M. Guerin in ascendiiig to Yentoux, who found a diminution in 

 summer 1° C. for 156 metres of ascent, while in contact this was for 

 195 metres. The comparison of the torrid with the temperate zone is 

 fallacious, as the results from the torrid zone were chiefly obtained 

 from the surfaces of high and extensive table-lands, while in Europe 

 they were made on more isolated and rapidly ascending ridges. 



Forbes gives numbers different from Arago ; and so does Ksemtz. 

 According to Forbes, there is a greater decrement in equatorial than in 

 temperate latitudes. He repeats the same remark at page 58 of the 

 same volume, Reports of the British Association for 1840. He also 

 quotes Biot in the Comptes rendus in support of the views put forward. 



From all the foregoing facts it may be concluded that the variation 

 of temperature with height is far from being correctly represented by 

 those who assume, for every part of the surface of islands and conti- 

 nents, a decrease of one degree Fahrenheit for every 300 feet of alti- 

 tude. So-called corrections of temperature made on this assumption 

 might be more truly called systematic interpolations of errors. But, 

 moreover, even if this arbitrary reduction were correct, it is not 

 justifiable ; for the object of temperature maps is to make manifest 

 the connexion between distribution of heat in the atmosphere close to 

 the ground with other phenomena, such as moisture and wind, or with 

 the distribution of plants and animals. All of these are influenced by 

 the actual temperatures, and not by the so-called corrected tempera- 

 tures for height. A map of the flora of a mountainous country would, 

 with the system of so-called corrections for height above the sea, 

 present the anomalous appearance of groups of Alpine or Arctic plants 

 touching the same isothermal lines as plants of temperate regions. 



The temperature maps of a continental country which, in some 

 respects, is circumstanced most nearly like the British Isles, namely, 

 Scandinavia, are instructive on this point. They have been drawn by 

 Professor Mohn of Christiania, and I have before me those which 

 accompany the beautiful work- of Dr. Schiibeler on the "Flora and 

 Plant Culture of Norway."^ They are constructed without the mis- 

 leading "correction" in height, which, in this case, would involve 

 the most absurd consequences as to the distribution of plants in rela- 

 tion to temperature. As in the British Islands, some of the isothermal 

 lines are closed curves, and most of the others resemble the general 

 outline of the Scandinavian peninsula. Among British botanists the 

 correct correlations of temperatui'e and plant distribution were long 

 since distinctly maintained at the International Botanical Congress in 

 London, when the late Dr. D. Moore and Mr. A. Gr. More exhibited a 

 map based on the distribution of temperature I had laid down in my 

 first memoir in the Atlantis.^ 



In the Journal of the Scottish Meteorological Society, Mr. Buchan 

 has collected an important series of facts as to the temperature of 



1 Norge's Vaextrige, 1st Bind. Chi-istiania, 1885. 



3 "On the Climate, Flora, and Crops of Ireland: Report of International Horti- 

 cultural Exhibition and Botanical Congress," p. 165. London, 1866. 



