366 



SCIENCE 



[N. S. Vol. LII. No. 1346 



to personal observation and inquiry extending 

 from Connecticut to as far north, as Hamilton 

 Inlet in Labrador. Tbe biology of the sub- 

 ject relates not so much to the habits of 8almo 

 solar as it does to the behavior of Hovio 

 sapiens — ^with his specific appellation self- 

 chosen. 



Egbert T. Morris 

 616 Madison Avenue, New Yoee 



efficiency in thermal phenomena 



To THE Editor of Science : Mr. Forbes's 

 theory of something being wrong with the 

 commonly accepted definitions of efficiency in 

 thermal phenomena, is provocative of com- 

 ment. The question of a definition being 

 wrong depends, obviously, on how it is inter- 

 preted. 



In general the efficiency of a machine or 

 mechanical process, is defined as the ratio of 

 output to input. It is assumed that the out- 

 put will always be less than the input, hence 

 the efficiency will be less than unity. 



It is safe to say that the difficulties alluded 

 to by Mr. Forbes can be traced to failure to 

 distinguish between the quantities of energy 

 called input and output, and the units in 

 which they are measured. In the electric 

 heater, the input, watts, is wholly converted 

 into heat, with efficiency of 100 per cent. In 

 the electric motor the input, watts, is converted 

 into 95 per cent, work and five per cent, heat, 

 giving 95 per cent, efficiency if work output 

 is considered, and 100 per cent, efficiency for 

 the entire output. In the steam engine the 

 input, heat, is converted into ten per cent, 

 work and 90 per cent, heat, giving an efficiency 

 of ten per cent, based on work output, 90 per 

 cent, efficiency based on the exhaust steam for 

 heating, and 100 per cent, for the entire out- 

 put. In the refrigerating machine the output 

 is, logically, heat carried away by the con- 

 denser water. The input, on the same reason- 

 ing, is made up of two parts, the heat removed 

 from the brine and the work of driving the 

 machine. The sum of the two input quanti- 

 ties is equal to the output, giving 100 per 

 cent, efficiency as in all the other cases. 



The refrigerating engineer recognizes the 



difficulty of applying the term efficiency to 

 his machine, and substitutes for it the term 

 " coefficient of performance," the ratio of heat 

 absorbed to the work required to drive the 

 machine, both expressed in the same units. 

 If efficiency is defined by the input-output 

 formula, it is true that the efficiency of all 

 machines is 100 per cent. If only a portion 

 of the input or output is considered, it is 

 possible to have efficiencies of less or more 

 than 100 per cent. In this case it would be 

 appropriate to use the term " partial effi- 

 ciency," since the entire output is not con- 

 sidered. 



E. H. LocKwooD 



THE HELIUM ARC AS A GENERATOR OF HIGH 

 FREQUENCY OSCILLATIONS 



Helium as a conducting medium in a low- 

 voltage arc may be of considerable utility as 

 a convenient source for generating, from 

 direct current, oscillations of moderately high 

 frequency. 



Due to its exceptionally low sparking 

 potential arcs may be readily started from a 

 hot tungsten cathode by 110 volts even when 

 the gas is at atmospheric pressure. In fact 

 it is easy to start the arc across a centimeter 

 gap between cold electrodes by means of 

 breaking a parallel circuit with a series react- 

 ance common to both. Perhaps a more con- 

 venient method of starting, however, is the 

 beating of the filament by the source of sup- 

 ply and then a commutation of the connec- 

 tion to the positive terminal from the fila- 

 ment to the anode. 



When the proper inductance and capacity 

 are connected across the arc high frequency 

 oscillations are produced which may be 

 utilized in the usual way with a coupled cir- 

 cuit. Hitherto, hydrogen and compounds of 

 hydrogen have been used in areas to produce 

 high frequency and it is very difficult to 

 produce oscillations by the use of other gases 

 at atmospheric pressure. Helium, however, 

 probably due to its high heat conductivity, 

 being inferior only to hydrogen in this re- 

 spect, from the rapid rate of energy dissipa- 

 tion in the arc, gives the type of volt ampere 



