388 NOTES OF A NATURALIST. 



we experience an increase of temperature in ascending above 

 the plain. The same result on a small scale may often be 

 remarked on clear cold nights, when the temperature rises for a 

 distance of some hundred feet in ascending isolated eminences, 

 the effect being due to the cooling effect of radiation from the 

 surface. 



It seems most probable that in the winter of the temperate 

 and polar zones the distribution of temperature in the atmo- 

 sphere is subject to conditions widely different from those 

 prevailing in summer ; and, if that be true, we should have 

 intermediate conditions in the spring and autumn ; so that 

 even if we could arrive at comparatively accurate results for 

 one season of the year, these would not be applicable at other 

 periods. 



The general result to which I have arrived is that to ascertain 

 the distribution of temperature in the atmosphere in successive 

 •zones of elevation is a problem of extreme complexity, towards 

 which the existing materials do not furnish even an approximate 

 solution. I hold, however, that it ought to be possible to obtain 

 much more definite knowledge than we now possess by means of 

 properly conducted observations in various parts of the world. 



Foremost of these I would suggest the importance of well- 

 conducted balloon ascents within the tropics. In selecting 

 stations for such ascents we are somewhat restricted by local 

 considerations, especially the extension of forests in many 

 regions, such as the greater part of tropical Brazil. In British 

 India there would be no difficulty in selecting suitable stations, 

 and there would be additional value in comparing the results 

 obtained from ascents in Bengal, and in the very different 

 climate of the North-west Provinces. Elsewhere in the tropics 

 we might expect valuable results from ascents in Queensland, 

 and from the llaiios of Venezuela. It seems not impossible 

 that, with a considerably smaller outlay, useful results may here- 

 after be obtained by means of improved self-recording instru- 

 ments sent up in captive balloons ; but in most countries such 

 a record would be liable to interruption owing to storms. 



The next desideratum is to obtain for a series of years simul- 

 taneous observations at successive stations, at vertical intervals 

 of 500 or 600 metres, situated on the flanks and at the 

 summits of high mountains to be chosen for the purpose. Some 



