722 COSMOS. 



mometer, and the rational deductions to be arrived at from its 

 indications, are as immeasurable as the sphere of those natural 

 forces which exercise their dominion over the atmosphere, 

 the solid portions of the earth, and the superimposed strata 

 of the ocean alike over inorganic substances, and the chemi- 

 cal and vital processes of organic matter. 



The action of radiating heat was likewise investigated, a 

 century before the important labours of Scheele, by the 

 Florentine members of the Academia del Cimento by remark- 

 able experiments with concave mirrors against which non- 

 luminous heated bodies, and masses of ice, weighing SOOlbs. 

 actually and apparently radiated.*" Mariotte, at the close of 

 the seventeenth century, entered into investigations regard- 

 ing the relations of radiating heat in its passage through glass 

 plates. It has seemed necessary to allude to these isolated 

 experiments, since in more recent times the doctrine of the 

 radiation of heat has thrown great light on the cooling 

 of the ground, the formation of dew, and many general 

 climatic modifications, and has led, moreover, through Mel- 

 loni's admirable sagacity, to the contrasting diathermism 

 of rock-salt and alum. 



To the investigations on the changes in the temperature of 

 the atmosphere, depending on the geographical latitude, the 

 seasons of the year, and the elevation of the spot, were soou 

 added other enquiries into the variation of pressure and the 

 quantity of vapour in the atmosphere, and the often observed 

 periodic results, known as the la w of rotation of the winds. 

 Galileo's correct views respecting the pressure of the atmo- 

 sphere led Torricelli, a year after the death of his great 

 teacher, to the construction of the barometer. It would 

 appear that the fact that the column of mercury in the 

 Torricellian column stood higher at the base of a tower 

 or hill than at its summit, was first observed at Pisa 

 by Claudio Beriguardi;f and five years later in France, 

 at the suggestion of Pascal by Perrier, the brother-in- 

 law of the latter, when he ascended the Puy de Dome, 

 which is nearly one thousand feet higher than Vesuvius. 

 The idea of employing barometers for measuring elevations 



* Antinori, Saggi dell' Accad. del Cim. 1841, p. 114, and in the 

 Aggiuntc at the end of the book, p. Ixxvi. 

 f Antinori, p. 29. 



