iv PREFACE 



sciences are of primary importance, moreover, physical laws 

 and principles are fundamental to all science, therefore they 

 form the major portion of this course. Microorganisms, how- 

 ever, play so large a part in the daily life of all people that the 

 principal facts concerning them are also presented. The main 

 study of animal and plant life has been left to be developed 

 as a course in general biology, or as special courses in botany 

 and zoology. 



The approach to each new topic is made from a historical 

 point of view, thus developing a real interest in the subject. 

 The course is progressive; the earlier chapters are relatively 

 easy; as the ability of the pupil grows, the course becomes 

 correspondingly more difficult. Numerous cross references are 

 given to stimulate frequent review. The teacher is urged to 

 insist upon the pupil's utilizing these references to past work. 

 It is not expected, nor is it desirable, that every school, or 

 every class in any school, shall study all the topics presented 

 in this text. Topics not essentially important in the environ- 

 ment of any class, or in the environment of the community, 

 may easily be omitted without seriously breaking the continu- 

 ity of the course. It is expected that the teacher will exer- 

 cise some judgment and discretion in omitting material from 

 this course which is least essential to the welfare of his par- 

 ticular class. 



Experience has shown that many of the exercises are best 

 conducted as class demonstrations wln'le a sufficient number 

 of them are well adapted to individual work. The apparatus 

 is, we believe, unusually inexpensive and is such as is to be 

 found in any fairly well-equipped laboratory, or it is of a com- 

 mercial type easily procured. The authors strongly advise, 

 however, that a few standard pieces of equipment, such as a 

 good barometer, a reliable air pump, a set of chemical ther- 

 mometers, a good microscope, etc., be purchased if not already 

 at hand. 



This text is a revision and enlargement of the Elements of 

 Physical Science published by the senior author in 1906. The 



