July 20, 1917] 



SCIENCE 



63 



Though I am reluctant to appear to adver- 

 tise dealers, for the convenience of readers 

 I think I am warranted in stating where the 

 materials mentioned in this article may be 

 purchased. The shade cloths may be pur- 

 chased from the Eemien and Kuhnert Co., 61 

 W. Grand Ave., Chicago. In September, 

 1916, I was given a price of 38 cents per yard 

 for "Peerless Cambric Ivory White" shade 

 cloth, 48 inches wide in entire rolls. The 

 price was 44 cents per yard in small quanti- 

 ties. The White Holland shade cloth was 

 slightly cheaper. Dr. G. E. LaEue, of the 

 University of Michigan, has informed me re- 

 cently that " Linaura Chart Cloth " sold by 

 the Williams, Brown & Earle Co., Phila- 

 delphia, is very satisfactory. 



For labelling, we are using a so-called " Sign 

 and Price Marker" set, No. 48 in catalogue 

 No. 28 of Meyer and Wenthe, 108 N. Dear- 

 born St., Chicago. The catalogue price is 

 $5.00 for the complete set. It is adapted to 

 charts to be used in large lecture rooms. Set 

 No. 6 at $4.00 and set No. 4 at $2.50 are 

 recommended for smaller rooms. The round 

 writing pens can probably be bought at many 

 art and drafting instrument stores. Mine 

 were obtained of A. H. Abbot and Co., 119 

 N. Wabash Ave., Chicago, i gross for 25 



E. M. Strong 

 Anatomical Laboeatories, 

 Vanderbilt IJNivEESirY Medical School 



THE ELEMENTARY TREATMENT OF FORCE 



The discussion by G. S. Fulcher in Science, 

 5LrV., 747, 1916, concerning some of the 

 errors and inconsistencies in our elementary 

 texts regarding the questions of force and 

 Newton's laws of motion, are most timely. 

 No doubt many of us who are trying to build 

 up in the minds of our beginning students a 

 sound structure of physical ideas, and above 

 all, are hoping through physics to give them 

 something of the scientific attitude, have 

 almost despaired of finding a text which is 

 free from the faults mentioned. To approach 

 the ideal, a text should be brief in its state- 

 ments but so explicit as to allow of but a 

 single interpretation; it should not anticipate 



knowledge which obviously the beginning stu- 

 dent does not possess, nor should it attempt to 

 circumvent this deficiency by repeatedly re- 

 ferring the student to articles further along; 

 it should, in fact, be written upon the premise 

 that the only source of physical ideas which 

 the average beginning student of physics has 

 is his own experience. 



In introducing force, therefore, all specula- 

 tion and conjecture, made in the light of the 

 author's own familiarity with the subject, is 

 decidedly out of place, and can serve only to 

 confuse the student. It should be presented 

 to him primarily in terms of his immediate 

 impressions, i. e., in terms of his muscular 

 sense. Let us tell him first that " force " is 

 the term applied to the equivalent of a push 

 or a pull. The average student has pretty 

 clear ideas as to what such an action can 

 accomplish. It is then not difficult to repre- 

 sent Newton's first law as a test for the ab- 

 sence of a force, nor the second law as a test 

 for its presence. After familiarity with these 

 notions has been gained, we can further repre- 

 sent the second law as a quantitative test for 

 force, and can show how we can experi- 

 mentally establish the relation / = ma. This 

 may then be regarded as a more exact defini- 

 tion of force, derived from our observations 

 upon objects external to omselves. In all of 

 this discussion it is of greatest importance 

 to emphasize by repetition the fact that when- 

 ever a force is exerted, two bodies are in- 

 volved: A, the body acting, and B, the hody 

 acted upon.''- This is one of the outstanding 



iln Ma reply (Science, XLV., 480, 1917) to A. 

 H. Patterson (Science, 5LV., 259, 1917), which 

 was printed after the present paper had been sub- 

 mitted for publication, Dr. Fulcher has already 

 emphasized this point. 



In this connection, may I suggest that we dis- 

 continue the use of the phrase, ' ' a force acts upon 

 . . ., " which is so exceedingly common in our 

 texts? It seems to me that the phrase attributes 

 to force a property which it does not possess. 

 Why not be unequivocal and say "a force is ex- 

 erted upon . . ."? This latter way of stating the 

 fact serves better than the former in keeping the 

 above italicized principle before the student, in 

 that it deprives the notion of force of that seeming 

 independence which does not pertain to it. 



