XVI ACKNOWLEDGMENTS 



Eyer and to Miss Ruth P. Kennedy, who have given great assistance 

 by drawing diagrams and doing other valuable work. 



The author wishes also to express his appreciation for the valuable 

 assistance rendered by Mr. Carl Voegelin of the Central High School, 

 Newark, N. J., who furnished the experiment on page 130 and who 

 read proofs; to Mr. S. A. Lottridge, East Orange High School, N. J., 

 who made valuable criticisms and suggestions; to Dr. Geo. Fitz- 

 simmons, Passaic, N. J., who read Chap. X; and to Mr. Roscoe P. 

 Conkling, Central High School, Newark, N. J., who has devoted many 

 hours to a painstaking and thoroughly constructive criticism, and 

 has in addition made many suggestions which have been of material 

 aid to the author in the preparation of this book. 



The author desires to mention Mr. Fred Beals, a true friend and 

 valued co-worker who died two years before work upon this book 

 was begun. At the time of his death Mr. Beals was working with 

 the author upon the outline of an Elementary Physics. Because 

 Mr. Beals was greatly interested in the subject of General Science 

 the author regrets that he was deprived of the sympathetic co-opera- 

 tion of one whose assistance and valuable criticism in the prepara- 

 tion of this book would have been of inestimable value. 



The author wishes to acknowledge the many courtesies of the 

 following, who have very kindly furnished cuts: 



Isko Corporation, Fig. 6; The Cedwin Co., Fig. 7; Taylor 

 Instrument Co., Figs. 8, 9, 10, 43, 44, 45, 46, 47, a, 6, c, 95, 96, 97; 

 Popular Science Monthly, Fig. 12; Encyclopedia Britannica, Figs. 

 31, 14, 15, 16, 17, 18, 19, 20, 21, 22; Standard Scientific Co., Figs. 

 34, 35, 62, 308; Child's Book of Knowledge, Foundation for, Figs. 

 38, 40; P. Blakiston & Co., Figs. 48, 77, 196; Tower, Smith & 

 Turton's Physics, Figs. 77, 48, 196; Denver Pressure Cooker Co., 

 Fig. 84; Duplex Fireless Cooker Co., Fig. 74; International Heater 

 Co., Figs. 83, 84, 86, 87, 138; (Veedol Oil), Platt & Washburn Co., 

 Figs. 98, 380; Pyrene Fire Extinguisher Co., Fig. 106; Foamite Fire 

 Extinguisher Co., Figs. 107, 108; Vacuum Oil Co., Figs. 114, 163; 

 U. S. Bureau of Standards, Figs. 117, 149, 260, 261, 262; Welsbach 

 Co., Figs. 121, 122, 123, 124, 125, 235; U. S. Department of Agricul- 

 ture, Figs. 126, 127, 128, 129, 130; Colgate Company, Figs. 143, 144; 

 American Medical Association, Fig. 145; Scientific American, Figs, 



