Xll 



TABLE OF CONTENTS. 



MAGNETISM. 



The magnet page 56 



The magnetic needle 56 



Degree of attraction 56 



Magnetic action 57 



Sir Isaac Newton's magnet 57 



Iron 57 



Magnetic attraction and re- 

 pulsion 57 



Dip of the needle 58 



Iron railings and carriage 



wheels page 58 



Cannon boring 58 



The magnetic power on the 



surface 59 



Wedgewood's black ware. . 59 

 Electricity and magnetism 59 



Chinese poles 60 



Aurora Borealis 60 



VARIATION OF THE COMPASS. 



Progressive motion of the 



variation 61 



Discovery of the variation 



of the compass 61 



Retrogradation of the varia- 

 tion 61 



Greatest variations 62 



Daily horizontal variation . . 62 

 Extent of the variation. ... 62 



Diurnal variation 62 



The magnetic equator .... 63 

 The north - west magnetic 



pole 63 



Movement of the magnetic 



pole 64 



Neutralization of the attrac- 

 tion of the ship's iron . . 64 

 State of the variation in 1825 65 



PNEUMATICS. 



Atmosphere 66 



Its constituent parts 66 



Extraneous ingredients .... 66 

 Height of the atmosphere . . 67 



Meteors 67 



Atmospheric changes 67 



Phenomena of the winds . . 68 



Effects of the winds 68 



Atmospheric pressure .... 68 

 Variation of the atmospheric 



pressure 68 



Specific gravity 69 



Evaporation and tempera- 

 ture 69 



A vacuum 69 



Barometer 70 



Barometric changes 70 



The wheel barometer of a 



syphon form 70 



The common barome- 

 ter 70 



Natural condition of the ba- 

 rometer 71 



Mensuration of heights .... 71 

 Mensuration of heights by 



the boiling point 72 



Cloudless elevations 72 



Origin of rain 72 



Rain 73 



Rain 73 



Rain at Oxford 73 



Rain in the Torrid Zone ... 74 

 Total weight, of the annual 

 rain 74 



