904 



SCIENCE 



[N. S. Vol. XLII. No. 1093 



The difficidty pedagogically is the defimtion 

 of the dyne, the force that gives a gram of 

 matter an acceleration of 1 centimeter per 

 second per second, and the fact that it has to 

 be translated into its equivalent in ordinary 

 language, a force of 1/980.665 gram, before a 

 clear concept of it can be obtained. If it had 

 been defined as the force which gravity exerts 

 on a gram of matter at 45 deg. latitude at the 

 sea-level, it would have been better. Prac- 

 tically the difficulty is that C.G.S. units de- 

 rived from the dyne are generally so small that 

 they usually have to be multiplied by a million 

 or more to make them usable, or to express 

 them in such terms as " the joule is 10' ergs," 

 and " the ohm is equal to 1,000,000,000 or 10^ 

 units of resistance of the O.G.S. system." 



It is not so difficult for one to break away from 

 the old units as may be imagined. A year 's con- 

 stant use of the C.G-.S. units makes one feel like 

 saying when reading of inch measurements ' ' Inch, 

 inch? "Where have we met that term before?" 



Of course it is not difficult for one who is 

 engaged constantly in the use of the C.G.S. 

 system, and who during that year has had no 

 occasion to use the old units, to break away 

 from them, but it is not only difficult but im- 

 possible, for a hundred million people who are 

 constantly using the old units to break away 

 from them. 



T. L. Porter and R. C. Gowdy, June 4 : 



We think Professor Kent has done well to re- 

 tain force and quantity of matter as equally 

 fundamental. 



Thanks ! I am glad of their company so far, 

 but I can not follow them in adopting the 

 " gravital " as a unit of acceleration. I in- 

 vented that term myself years ago, as a dis- 

 tance of 32.2 feet, only for the purpose of using 

 it as a "horrible example." I fear now that 

 some one else will adopt my "timal," 1/32.2 

 of a second. Still less can I accept their micro- 

 speedal or their six Greek letter constants. 

 Perhaps my sense of humor is lacking, in fail- 

 ing to recognize that their article is a joke and 

 a satire, but it reads as if they seriously mean 

 all they say. Here are some brief quotations 

 from their article. 



Let TV = matter in pounds. 

 F := force in pounds. 



Mass shall be an exact equivalent for quantity 

 of matter. 

 Weight means the gravitational force upon a mass. 



The measure of a force may be defined by the 

 equation F = ma. 



There are 32.2 of the units of force defined by 

 F = ma in a pound weight. 



What is the unit of m if not the slug? 



We frankly talk about a unit of force called the 

 poundal. 



If I understand this rightly Messrs. Porter 

 and Gowdy measure matter in both pounds and 

 in slugs, and force in both pounds and in 

 poundals, and to my mind this only increases 

 the existing confusion. 



I have just looked over the solution of my 

 problem and I find that it contains twelve 

 technical terms, including one constant, viz., 

 force, pounds, matter, seconds, velocity, dis- 

 tance, acceleration, impulse, momentum, 

 energy, work ; g = 32.1740. 



Messrs. Porter and Gowdy's article contains 

 the same twelve, and also fourteen additional 



mass. 



ones, VIZ., micro-i 

 weight, poundals, slugs, pounds-weight, unit 

 and six Greek letter constants. The object of 

 my work has been to eliminate as many use- 

 less terms as possible, with the view of making 

 the subject of dynamics easier. Their object 

 seems to be to use as many terms as possible. 

 I wish they woiild give my problem to a class 

 of their students, and ask them to take it home 

 and bring in written solutions in the method 

 in which they have been taught. The prob- 

 lem for this purpose might have added to it 

 one to be solved arithmetically, such as a 

 1,000-lb. boat is pulled with a force of 1 lb. for 

 4 seconds. Assuming that frictional resistance 

 may be neglected, find the distance, velocity, 

 acceleration, etc. 



Paul F. Gaehr, June 25 : 



I say that we may take as our unit of force 

 that force which gives to unit mass a unit accelera- 

 tion. Let us fetch that backward baby, the 

 poundal, into the room for an inspection at least 

 long enough to learn that the weight of a pound 

 is 32 poundals. 



Yes, we may inspect that backward baby a 



