VI PREFACE 



The directions for field and laboratory work have been 

 grouped together in a separate booklet, thus making it easy for 

 the teacher to assign lessons or modify the work. This also 

 makes unnecessary the presence of textbooks in the laboratory. 

 Throughout both the laboratory manual and the textbook a too 

 rigid plan has been avoided, and it is therefore expected that 

 each teacher will be able to express his own ideas regarding 

 the sequence of subjects and the phases of the work to be 



emphasized. 



ROBERT W. HEGNER. 



ANN ARBOR, MICHIGAN, 

 January, 1915. 



