902 



SCIENCE 



[N. S. Vol. XLII. No. 1095 



of it. I hold that the standard weight of a 

 body is the number of pounds of force re- 

 quired to give the body the acceleration 32.1740 

 ft. per second, whether that is the earth's 

 gravitational attraction on the body at the 

 standard locality or whether it is the force re- 

 quired to slide it along a frictionless plane 

 with the same acceleration. It is also the 

 measure of a " body-constant," viz., the con- 

 stant quantity of matter in the body, as deter- 

 mined by weighing it on an even balance 

 scale, which is quite independent of the value 

 of the force of gravitation at the place where 

 the weighing is done. The quantity of matter 

 might also be determined by multiplying its 

 volume by its specific gravity, or, if its specific 

 heat were known, by finding how many de- 

 grees it would heat a given volume of water. 

 Por example, a piece of iron in cooling 100 

 deg. F. heats a cubic foot of water 1 deg., 

 what is its weight, the specific heat of the iron 

 being 0.111, and 62.36 British thermal imits 

 being required to heat a cubic foot of water 

 one degree ? Answer, 62.36 h- (100 X 0.111) = 

 5.62 lbs. 



In other words, weight, or standard weight, 

 is both a quantity of matter and a force. 

 "While matter and force are two entirely differ- 

 ent things, force being a push or a pull and 

 matter something that may be pushed or 

 pulled, the quantity of matter in a body may 

 be determined by finding how much force is 

 required to lift it. Both the quantity of the 

 matter and the amount of force are called the 

 weight of the body. They are different things, 

 but niunerically they are the same. The 

 weight of a 1 lb. weight (piece of metal) is one 

 pound, that is there is a pound of matter in it, 

 and the force required to lift it is also called 

 its weight and is a pound, of force (not a 

 pound-weight, with or without the hyphen, for 

 that is a term that is properly applied to a 

 piece of metal used for weighing other bodies). 



This double definition of the word weight is 

 sanctioned by a thousand years of usage. It 

 is universal in literature and in commerce. 

 In the vain attempt to get rid of it the text- 

 book writers have substituted the word " mass " 

 for weight, meaning quantity of matter, and 



tried to confine the word weight to mean the 

 amount of gravitational force acting on a 

 body ; but the great public will not have it so ; 

 they will continue to call both the force and 

 the quantity of matter by the good old word 

 weight. Then the text-book writers thought 

 it would be a good thing to hybridize the 

 C.G.S. system with the English system of 

 weights and measures, and say unit force is 

 that force which gives unit mass unit accelera- 

 tion, and they invented the poundal to achieve 

 this result ; then, that device leading to trouble 

 and confusion, they invented the gee-pound or 

 slug and so increased the trouble. 



In fact it (a supported body) has an accelera- 

 tion even though at rest relatively to the earth. 



I do not understand Professor Hoskins here. 

 If acceleration means change of velocity 

 divided by time, and rest connotes no change 

 of velocity and no velocity, how can a body at 

 rest on the earth's surface have an acceleration 

 relatively to the earth, that is radially toward 

 the earth's center, or relatively to a fixed point 

 in space, if there is no change in the speed of 

 rotation of the earth? 



Professor Hoskins, May 7: 



Mr. Kent's equation V=^KFT/W is entirely 

 satisfactory and sufficient so long as our study is 

 confined to the cause in which a force whose di- 

 rection and magnitude remain constant acts upon a 

 body otherwise free and initially at rest. This is, 

 however, a very exceptional case. The funda- 

 mental principle in its generality can be expressed 

 only by introducing the notion of instantaneous 

 rate change of velocity, i. e., acceleration. 



I am glad that Professor Hoskins admits 

 the sufficiency of the equation for the partic- 

 ular case to which I applied it, that of the body 

 initially at rest acted on by a force constant 

 in magnitude and direction. I call this equa- 

 tion fundamental because it is derived from 

 experiment with the Atwood machine or other 

 apparatus, and because it is a foundation upon 

 which other equations may be built. Now let 

 us build on it to arrive at the general case, by 

 removing the restrictions of the original prob- 

 lem. Take unit force as the force which act- 

 ing for one second gives a pound of matter a 

 velocity of 32.1740 feet per second, then the 



