54 THK AGE or PERICLES. 



will amount to thirty degrees, and thns the difference, within certain 

 limits, will be in proportion to its height. The specific gravity of a 

 cloud, also, of any height, compared with that of the surrounding air at 

 the same elevation, may be calculated, when the dew-point is given; 

 for its temperature is known by experiments with the Nephelescope, and 

 the quantity of vapoi condensed by the cold of diminished pressure at 

 every point of its upward motion, and of course the quantity of caloric 

 of elasticity given out by this condensation is known, and also the ef- 

 fect this caloric has in expanding the air receiving it, beyond the volume 

 it would have if no caloric of elasticity was evolved in the condensa- 

 tion of vapor. It will readily be perceived how the respective specific 

 gravities of two bodies of air will be affected by their difference of tem- 

 perature, and how, apart from other powerful causes, the barometer is 

 caused to fall by the great expansion of the air in consequence of the 

 immense evolution of latent caloric, and that, too, in proportion to its 

 heio-ht. It will, also, be perceived how the heat, which is set free in 

 the cloud, must accelerate the velocity of the upward motion, and com- 

 municate to the storm a steam power of great force, also proportionate 

 to its height. 



If, therefore, we know the temperature of the air, and that of the 

 dew-point, we can calculate from the laws already laid down, the height 

 of the base of the cloud, the amount of the vapor deposited there, the 

 temperature and amount of vapor and its elastic force above the base, 

 and the quantity of rain it must discharge. It certainly is most beauti- 

 ful and surprising, that the thermometer, which was invented merely to 

 ascertain the temperature of bodies, should reveal so much ! 



THE AGE OF PERICLES. NO. I. 



Thucydides informs us that the ancient Grecians were a rude and 

 warlike people, subsisting mainly upon the booty taken from their 

 neighbors. In the progress of time, they united their scattered habita- 

 tions and built cities, locating them for the sake of security on peninsu- 

 las, and surrounding them with walls. Gradually the unwalled towns 

 and feebler cities yielded to the invasions of the more powerful, and 

 being united to them, constituted what might be called the first form of 

 empire. In this state of affairs, the Trojan war occurred. The ten 

 years whicli were spent in this memorable siege would naturally pro- 

 duce, in such unseulcd times, very important changes. Conquests were 

 made at home, as well as attempted abroad ; and many of those who 

 rubhcd into the contcbt at the tiummons of Agamennion and burned to 



