6 Introduction. 



ating every science and every art to show that there is a 

 physics of each or a necessary treatment of them from the 

 standpoint of mechanical principles of matter and energy. 

 Physics, therefore, a broad science, is one of wide applica- 

 tion and fundamentally important to the understanding of 

 almost any concrete subject when treated from the stand- 

 point of cause and effect. 



2. Matter and Force. So far as we are at present able 

 to comprehend, the various phenomena of nature are mani- 

 festations of two classes of agencies, matter and force. The 

 river flowing steadily toward the sea is a mass of matter 

 urged continually onward by the force of gravitation. Coal 

 and oxygen burning in the firebox of the locomotive are two 

 forms of matter urged into motion by the force chemical 

 affinity. The time-keeping watch is a mechanism jf brass 

 and steel kept in uniform motion by the force cohesion un- 

 coiling the wound-up spring; and tLe capillary rise of oil 

 in the lamp wick and of water through the soil are other 

 movements of matter actuated by the same force. 



3. Constitution of Bodies. All bodies or masses of mat- 

 ter with which, we are acquainted possess such properties 

 as to make it appear that there is room in them not occu- 

 pied by the essential material which makes up the body. 

 They are made out of definite units which have been 

 named molecules much as a bank of sand is composed of 

 grains or as a sack of shot is filled with spheres of lead. 



The openness of structure of all bodies is a very impor- 

 tant conception to have clearly in mind. It is this open- 

 ness of structure which makes it possible for foul odors 

 to be absorbed by milk or drinking water; for moisture 

 to enter sprouting seeds ; for the food we eat to pass through 

 the walls of the alimentary canal to enter the blood vessels 

 and out of these again to the muscles and nerve centers. 

 It is the openness of structure of the lung lining which per- 

 mits the oxygen of the air to enter the system and the car- 

 bonic oxide to escape from it ; and were it not for this struc- 



