66 GENERAL SCIENCE 



of gas placed in a closed vessel will take the shape of the 

 vessel and also fill it, because the molecules move in 

 every direction with great speed. It is the continuous 

 hammering of these millions of molecules on the sides of 

 the containing vessel that produces what is known as 

 gas pressure. The pressure due to the molecules of a 

 gas hitting the sides of the vessel or gas pipe could be 

 illustrated by letting a stream of small lead shot fall on 

 a balance scales. It would be found that the force of 

 the stream of shot would be proportional to the number 

 of shot striking the balance per second, if their speed is 

 kept constant, which could be done by permitting them 

 to fall from the same height. The pressure of a gas is 

 proportional to the number of molecules striking the 

 sides of the containing vessel per second, if their speed is 

 kept constant. Their speed is dependent upon their 

 temperature. 



From the chapter on Chemistry of Common Things we 

 learned that all matter is composed of molecules. Com- 

 plex molecules are composed of two or more atoms. 

 Atoms are composed of electrons or ions. By great scien- 

 tists, such as Professors Millikan and J. J. Thompson, it 

 has been found that the electron is only a charge of elec- 

 tricity, and when the electric charge is removed no weight 

 is left. Hence atoms are composed of a number (varying 

 from 700 in hydrogen to 160,000 in radium) of electrical 

 charges so arranged that they are not easily moved out of 

 their sphere of activity. Atoms compose molecules, and 

 hence molecules are composed of charges of electricity. 

 All matter is composed of molecules; therefore, matter is 

 electricity. 



49. Gravity. Gravity is the force with which the 

 earth draws objects toward its center or holds objects 



