THE ATMOSPHERE. 71 



signals so arranged, is used in the manner thus de- 

 scribed. 



The diving bell has been applied to many useful pur- 

 poses, as the construction of marine works, the eleva- 

 tion of sunken vessels, and the recovery of treasures 

 from the bottom of rivers. 



But one of its most singular applications, has been in 

 blasting rocks at a considerable distance under water. 

 At Howth, in Ireland, persons descended, and drilled 

 and charged the rock, and carried up a tin tube to the 

 surface, through which the fire was to be applied. This 

 was done by dropping a piece of red hot iron down upon 

 the powder. 



CONCLUSION. 



There is no subject of natural philosophy more inter- 

 esting than the one we have just considered. It presents 

 so many beauties, and so great a variety, that we are 

 surprised that a substance with which we are so familiar 

 can possess such features. 



Until Philosophy began her researches mankind knew 

 nothing of the subtile fluid which surrounds the earth, 

 and which extends so far from its surface. They had 

 no idea of the effect of respiration ; why a flame was 

 enkindled by forcing a current of air through a dull fire, 

 and why fermentation was facilitated by an exposition 

 to the atmosphere. They enjoyed the delightful breeze 

 which gathered the night-dew from the flower, and 

 passed along laden with its fragrance ; but the power 

 of the air was only known to them in the wind, which in 

 its fury lashed the ocean into foaming billows, and swept 

 down the trees of the forest and the habitations of men. 

 They knew nothing of the air but by its effects, as the 

 child observes the motion of the hand of the clock, with' 1 

 out comprehending its cause. 



There is something peculiarly interesting in the dis- 

 covery of causes. Effects with which we are familiar 

 soon cease to excite attention, even when the subject is 

 stupendous ; but when we have traced anything, how- 

 ever simple, to its first cause, we experience delight 



