854 



SCIENCE 



[N. S. Vol XLIII. No. 1120 



Energy may be defined as work whieli is stored 

 up. Work stored up in overcoming kinetic reac- 

 tions is called kinetic energy. Work stored up in 

 overcoming non-frictional forces, such as gravita- 

 tional forces, is called potential energy. "Work 

 done in overcoming frictional forces is called heat 

 energy. 



Potential, kinetic and heat energy are different 

 (at least apparently^) forms of the same physical 

 entity, i. e., energy. Energy may be changed from 

 any one of these forms into any other form. 

 Whenever such a change takes place energy is 

 said to be transformed. Transformation of energy 

 is always accompanied by work. In fact the 

 process of doing work is that of transformation of 

 energy. The amount of energy transformed equals 

 the amount of work done.s 



Yale Univeksity 



units of force 

 To THE Editor of Science : I have read with 

 much interest Professor Kent's article in 

 Science on the units of force. I might say 

 that I have taught mechanics in my physics 

 course this year, using the units the way Pro- 

 fessor Kent recommends. The results have 

 been entirely successful and highly gratifying. 

 I used the pound and the gram as the units of 

 mass and the pound and the gram as the 

 units of force. As far as the results to the 

 student go it has resulted in conciseness and 

 clearness of thought and an avoidance of the 

 unescapable confusion that results from in- 

 troducing units that nobody but a teacher of 

 physics wishes to use. liot only did this apply 

 to force equations but it had a good result all 

 along the line in problems on work energy 

 and power. I embodied in my method of 

 teaching the things that Professor Kent rec- 

 ommends and also many of the things that 

 Professor Huntington recommends. I be- 

 lieve that a great deal of the trouble is due to 

 the fact that most of our teachers of physics 

 do not have the point of view of the engineer 

 (they should have if they teach engineers) and 



2 Eecent developments in physical sciences tend 

 to show that differences between different forms 

 of energy are only apparent and that all forms of 

 energy are, in the last analysis, kinetic. 



3 H. M. Dadourian, "Analytical Mechanics," 

 2d edition, p. 248. H. M. DaDOUBIAN 



I believe that the only way to get this point 

 of view is in the school of practical engineer- 

 ing. This hodgepodge of units which some of 

 us wish to use are undesirable and pedagog- 

 ically unsound. 



Paul Oloke 



thermometer scales 

 To THE Editor of Science : In a letter pub- 

 lished in Science of May 5, 1916, page 642, a 

 correspondent advocating the retention of the 

 Fahrenheit scale says that " nine tenths, prob- 

 ably, of the use of the thermometer is for the 

 weather " a statement that should not pass 

 unchallenged; but even if there were no other 

 uses of the thermometer, the Fahrenheit scale 

 would still be objectionable. If your corre- 

 spondent will visit any extensive meteorolog- 

 ical library, he will find that nearly all national 

 weather services now use the Centigrade scale 

 and that internationally no other scale has 

 been recognized for some years. Even the few 

 weather services retaining the Fahrenheit 

 scale, restrict its use and banish it from all 

 investigational and research work. 



It is urged that " the common people are 

 familiar with the Fahrenheit scale." They 

 may be familiar with it and yet not under- 

 stand it. When the temperature is 64° F., is 

 it clearly understood by every one, that the 

 temperature is 33 degrees above freezing; 

 and on the other hand when it is — 32° F., 

 that the temperature is 64 degrees below freez- 

 ing? The scale says one thing and means an- 

 other. It is true that the Centigrade scale divi- 

 sion is nearly twice the length of the other 

 scale division ; and much has been made of this 

 by some who insist upon accuracy to the tenth 

 of a degree; but it may be well to remember 

 that most air temperatures are a degree or 

 more in error. Even with official instruments, 

 errors of erposure or time, exceeding several 

 degrees, go uncorrected, while instrumental 

 errors are applied to a tenth of a degree. On 

 the daily weather map one finds isotherms 

 charted from readings made at different hours 

 and diilerent elevations. A reading made at 5 

 A.M. in the Nevada desert is linked up with 

 readings made at 8 A.M. on the Atlantic sea- 

 board. Some years ago, I suggested to the 



