392 



SCIENCE 



[N. 8. Vol. XXXIX. No. 1002 



make the correction now at a time when we 

 are trying to break away from the old order, 

 attempting to introduce rational units in place 

 of the old arbitrary ones. It is somewhat em- 

 barrassing for one who has advocated the 

 introduction of absolute units to acknowledge 

 the validity of the criticism of chemist, 

 physicist and engineer; but fortunately the 

 corrections can be made readily by changing 

 the millibar of the aerologist to kilobar. In 

 the conversion tables which are in course of 

 preparation, this will be done. 



Briefly, the term " barad " was proposed by 

 a committee of the British Association for 

 the Advancement of Science, 1888, as a 

 suitable term for the unit of pressure, one 

 dyne per square centimeter. Some years later 

 Ostwald advocated the use of one million of 

 these units as the standard, but gave the 

 standard no name. The term har was pro- 

 posed by Richards in 1903 for the small unit of 

 pressure, one dyne per square centimeter; and 

 megahar for a C.G.S. atmosphere. So far as 

 I can ascertain this is the first case in which 

 a clear-cut definition of an absolute atmos- 

 phere has been used in actual investigation. 

 He has consistently used this unit megabar as 

 the basis of his work ever since. Eichards's 

 atmosphere is 0.987 of the ordinary sea-level 

 atmosphere or 1.020 kilograms per square 

 centimeter; and under the new order agrees 

 with the standard level of Koppen, the million- 

 dyne level at about 106 meters elevation. 



It seems almost unnecessary to argue that 

 the smaller bar should be the basic unit and 

 not some multiple. And again it is doubtful 

 if bar is tlie best designation for the pressure 

 of an absolute atmosphere. Megabar is not 

 altogether inappropriate and has priority of 

 usage especially in the literature of chemistry. 

 A megabar in the aerologist's notation would 

 be the pressure of a million atmospheres, a 

 magnitude not often dealt with. On the other 

 hand, we often need to refer to pressures 

 smaller than the millibar of the aerologist. 

 The bar of the chemist and physicist is con- 

 veniently divisible down to its millibar, i. e., 

 a thousandth of a dyne per square centimeter. 



The following table contrasts the two sys- 



tems. At Dr. Richards's suggestion it is re- 

 stricted to those terms most likely to be used. 



Chemist'B and 



Physicist's (to FormerAerolo- 



be Universally gist's (to be 



Used Hereafter) Abandoned) Remarks 



1 megabar One million atmos- 

 pheres, far beyond our 

 present possibilities of 

 direct measurement. 



1 megabar 1 bar The absolute atmos- 



phere; equal to 750.1 

 mm. mercury or .987 

 usual sea-level atmos- 

 phere. One megadyjie 

 per square centimeter 

 acting through one cubic 

 centimeter does one 

 megerg of work. 



1 kilobar 1 millibar One kilodyne per square 



centimeter. 



1 bar ? One dyne per square 



centimeter acting throua;h 

 one cubic centimeter 

 does one erg of "work. 



There would be no objection to giving the 

 term megabar or absolute atmosphere some 

 convenient nickname such as " aer " if mega- 

 bar is too ponderous. It has been suggested by 

 Professor Richards that for historical reasons- 

 the pressure of 10,000,000 dynes (ten abso- 

 lute atmospheres) might be named after some 

 pioneer in meteorology, as Guericke or Torri- 

 celli, after the analogy of the " watt," " joule,"' 

 " ampere," etc., but this need not be insisted 

 on at present. 



Alexander McAdie 



Blue Hill Observatory, 

 February 28, 1914 



ACADEMIC ELECTIONS 



To THE Editor op Science: In connection 

 with the table of percentages accompanying 

 my article on " Academic Student Elections,"' 

 in Science for January 16, a correspondent 

 has called my attention to some inaccuracies 

 in copying percentages from Professor Ferry's 

 tables, on which the article was based. 'With 

 one exception they do not seem very impor- 

 tant. This exception is in connection with 

 the work in biology at Bowdoin College. The 

 entry was from the wrong column of Professor 

 Ferry's extended table, and to Bowdoin was 

 assigned the lowest record in this subject. A 



