SUPPLEMENTARY REPORT ON METEOROLOGY. be 
the British government, continued for a series of years on this 
account. M. Boussingault has remarked, that at the Equator 
the mean temperature of any place may be found at any time of 
the year, and at any hour of the day, by digging a pit in a 
shady spot a foot deep, and observing the temperature at the 
bottom of it*. M. Poisson considers this result as conform- 
able to theory}. It is, at all events, a most convenient fact, 
and adds one to the many encouragements which nature affords 
to the prosecution of meteorology in tropical regions, where 
hitherto it has been most neglected. 
50. The improvement of our knowledge of terrestrial tempe- 
rature is a most important branch of science. It may be doubted 
whether it has hitherto been cultivated in the right way, and 
whether local and minor anomalies have not been allowed to 
conceal the general laws which we should first seek to attain. 
It is quite certain, that the causes producing the inflexions of 
the isothermal lines are of the most irregular and unmathe- 
matical character, such as the boundaries of coasts and the like. 
Still we think that the time may not be far distant when we 
shall have isothermal charts as superior to those now existing, 
as Gauss’s magnetic charts, deduced by skilful artifices from a 
limited number of good observations, are to those of Halley in 
the last century. 
D. Decrease of Temperature with Height}. 
51. Part of what properly belongs to this head will be more 
conveniently treated of in considering the general question of 
the temperature of the globe and its appendages. 
52. There is little doubt that the decrement of temperature 
is not uniform, but slower as we ascend. It is to this, pro- 
bably, that we are to ascribe the greater values of the height 
due to 1° of decrement in equatorial than in temperate climates: 
thus, Boussingault found 26° c. of decrement for 4800 metres 
of ascent in the tropics, or . . 1°c. for 184 met. 
Col. Sykes, in India, on a height of 
8500 ft., finds 1° F. for 332 ft. of 
ascent §, or . . : 5 RP gore a =) 
Whilst Saussure’s mean value in the 
Alps is : § j erie yy 154 -'53 
Eschmann on the Rigi. F Sede Copibet ag Wy Uae As 
* Ann. de Chim. liii. Annuaire, 1836, p. 263. 
+ Théorie de la Chaleur, p. 508, &c. 
t See First Report, p. 218, and Mahlmann, p. 53. 
§ British Association, Fourth Report, p. 568. 
