ma CMCB 



42 FIRST TEAR SCIENCE 



It was the arrangement of the tiny magnetized particles 

 which must have caused the contents of the tube to be- 

 come magnetic. It would therefore seem prob- 

 able that magnetism must be a property of the 

 exceedingly small particles or molecules of which 

 the iron or steel as well as all other substances 

 are supposed to be composedo 



It is supposed that when a bar of 

 steel becomes magnetized the mole- 

 cules arrange themselves in definite 

 directions, as do the filings in the 

 tube. The molecules of magnetic sub- 



.... 



eeii 

 .... 

 .... 



BOBB 

 Biii 

 BiiE 

 .... 

 .... 

 .... 



BEBB 

 .. .. 



Fig. 17. stances are supposed to be separate 

 little magnets. In the unmagnetized 

 bar (Fig. 17) their poles point in all directions 

 dependent upon their mutual attraction, and 

 thus they neutralize each other. When the bar Fi lg 

 becomes magnetized the molecules tend to ar- 

 range themselves so that like poles lie in the same direc- 

 tion (Fig. 18). When the magnet is heated or jarred 

 the molecules are moved out of this alignment and the 

 magnetism is weakened. 



Summary. The shape of the earth is spherical with 

 very slight flattening at the poles. Its diameter is almost 

 8000 miles, more than four times the distance from New 

 York to Denver ; and its circumference is nearly 25,000 

 miles. Though the irregularities of the earth's surface 

 are exceedingly small in comparison with its total area, 

 they are great enough to have a vast effect upon the life 

 of animals and plants. 



The revolution of the earth upon its axis causes day 

 and night, and gives us our measurement of time and our 

 points of the compass. The movement of the earth 



