182 Col. R. Wright's Meteorological Observations in Colombia. 



Popayan, Poblason, 



Juntas, Buenavista, 



Paisbamba, Hevradura, 



Sombreros, Pasto, 



Tambores, Quito. 



Estrellas, 



Memoria, S^c. p. 13, et seq. 

 Working upon the foregoing principle, Caldas adapted to 

 his thermometer a barometrical scale. The product of 0°*97'i 

 of Reaumur by 19 is 18-506, oi", in round numbers 18*5, i.e. 

 18°'5 of Reaumur correspond to 19 inches of the barometer. 

 Then measuring 1S*5 from the summit, or 80° of Reaumur's 

 scale, he transferred it to the opposite side of the thermome- 

 ter, dividing it into 19 equal parts, or inches of the barome- 

 ter, subdividing these by a nonius into 24 each = half a line 

 of the barometer. In this manner the elevation of the ther- 

 mometer by boiling water indicates the corresponding eleva- 

 tion of the barometer under the same atmospheric pressure. 

 Caldas observes that Humboldt, to whom he had communi- 

 cated these ideas, when they met in Popayan, objected the 

 variability of the heat of boiling water under the same atmo- 

 spherical pressure; to which he replies: " Long practice has 

 taught me its invariability in this respect, using the requisite 

 precautions in making the experiment : otherwise, how could 

 there be equal thermometers ? Is not the invariability of the 

 heat of boiling water under the pressure of 28 inches the found- 

 ation of the superior term of all thermometrical scales? It 

 is true that boiling water does not immediately acquire its ex- 

 treme heat, but pushing the operation to its maximum its heat 

 is always the same." p. 24. 



Caldas did not consider an invariable exponent possible, 

 on account of the variability of atmospheric pressure. The 

 want, however, of a barometer induced me to make some ex- 

 periments to this effect, by way of rendering this method of 

 measuring elevations still more simple, and of more general 

 use. Is the variability of atmospheric pressure such as to 

 make any important difference in these calculations ? Does 

 not water boil constantly at 212^ at the level of the sea? At 

 Quito I found the same result as Caldas had several years 

 before ; and several times the same result in this and other 

 parts of the Andes. The difference, then, is scarcely percep- 

 tible in the thermometer, and consequently unimportant in 

 the results of a calculation founded on the heat of boiling 

 water. The thermometer besides, immersed in boiling water, 

 is less liable to a variety of atmospheric influences to which 

 the mercury of the barometer is necessarily subject. Hence 



