1912^ Fundamental Bases of Dynamics 69 



and it is well as a preliminary to the subject of dynamics to 

 precisely describe the two methods of weighing and under what 

 conditions they differ. 



In what follows, the writer desires to acknowledge his indebt- 

 edness to an article by Prof. William Kent in " Science" for 

 May 5th, 1911, entitled, " N^otes on the Preliminary Report of 

 the Committee on the Teaching of Mathematics to Students of 

 Engineering." The present article might very well bear the 

 same title, for its inspiration has come through reading the 

 parts of the report given by Professor Kent and his valuable 

 criticism thereon. The great value of the Report and E^otes in 

 outlining a method of presenting the first principles of dynam- 

 ics, is acknowledged. But the writer believes the matter can be 

 cast into a simpler and more logical form and he will endeavor, 

 in what follows, to carry out this idea by suggesting such an out- 

 line of parts of the subject where amendment seems desirable. 



(1) Mechanics treats of matter, at rest or in motion, under 

 the action of force. 



(2) The phrase, "weight of a body," is unfortunately used 

 in two senses ( 1 ) to indicate the quantity of matter in the body, 

 (2) to mean the force of attraction of the earth at the place on 

 the body. To avoid confusion it is often advisable to specify the 

 meaning intended. Thus a piece of matter weighing a pound 

 may be called a pound of matter or a pound mass, whereas the 

 force of attraction of the earth on it will be called a pound force. 

 Similarly we can speak of a ton of matter and a ton force. 



(3) The "British Unit" of weight is the quantity of matter 

 in a certain piece of platinum and is called a pound. The 

 "French Unit" is called the kilogram. 



Copies of either standard, together with multiples and frac- 

 tional parts of the same, will be called "a set of standard 

 weights." 



(4) To weigh a body on an equal armed balance, the body is 

 put in one scale pan and is balanced by a certain number of 

 standard weights (metal pieces) in the other scale pan. By this 

 method, it is seen that the body will "weigh" the same at any 

 latitude or altitude. Since the attraction of the earth on a 



