268 



SCIENCE 



[N. S. Vol. XLVII. No. 1211 



strictly to the true thermodynamic scale. In 

 fact, the general requirements of science are 

 very often largely met by the use of an ap- 

 proximate absolute scale which, for the centi- 

 grade system, is defined by the equation 

 T = 273. + t° Cent. 



The observed quantity, t°, may be referred 

 to the normal hydrogen centigrade scale or 

 be determined by any acceptable thermometric 

 method. This approximate scale is often 

 called the " absolute " or the Kelvin scale, 

 perhaps for tlie sake of brevity or convenience. 

 Of course, no one can disregard the technical 

 differences between the real and false or ap- 

 proximate, absolute scale. 



Such a scale differs from the true Kelvin 

 scale, first, because 273° is not the exact value 

 of the ice point on the Kelvin scale ; second, be- 

 cause each observed value of t° other than 0° 

 or 100° requires a particular correction to 

 convert it to the corresponding value on the 

 Kelvin scale. These corrections will differ 

 according to the kind of thermometer used in 

 obtaining the value t° and while they are 

 small for temperatures between 0° and 100° 

 they are large at extreme temperatures and are 

 important in all questions involving thermo- 

 metric precision. 



The approximate absolute scale is sufficiently 

 exact for nearly all purposes, it is most con- 

 venient in computations and in the publication 

 of results; further, its numerical quantities 

 are strictly homogeneous, and should any nec- 

 essity arise data published in its imits may 

 be readily reduced to the absolute Kelvin scale 

 by simply applying the appropriate correction 

 for the zero point of the scale — about 0.13° 

 C. — and the other appropriate correction to 

 reduce the observed temperature, t°, to the 

 true thermodynamic temperature. It is thus 

 clear that much confusion and imcertainty of 

 terminology and meaning would be obviated 

 and Kelvin's suggestion properly appreciated 

 if scientists would agree to give the approxi- 

 mate absolute scale a particular name of its 

 own and reserve the name " absolute " for the 

 scale that is truly absolute, viz., Kelvin's ab- 

 solute thermodynamic scale. 



In accordance with the foregoing ideas, the 

 thermometric scale and nomenclatvu:e in the 

 centigrade system may be set forth in the 

 following maimer : 



THERMOMETRIC NOMENCLATURE 

 AS IT IS 



Fiducial Points 



Centigrade scale Freezing Boiling 



Normal hydrogen constant-pres- 

 sure thermometer 0° 100° 



Thermodynamic scale 



Absolute scale 



Kelvin scale 



Approximate or ' ' near-abso- 

 lute" scale defined by the 

 equation — 



T = 273 + f Cent 



All frequently 

 loosely designated 

 Absolute Scale 

 in scientific litera- 

 ture. 



AS IT SHOULD BE 



Centigrade scale 0° 100° 



Thermodynamic scale 1 o j.^^-^'!?" ^^^•^^'' 



Absolute scale I Strictly synony- 



Kelvin scale f ™ou? /"^d strictly 



J one ideal scale. 

 "Approximate-'absolute (?)".... 273° 373° 



Let us prevent confusion and uncertainty, 

 make the meaning of scientific writings clear 

 and distinct, by giving an appropriate name 

 to the scale 



2" = 273 -|-«° Cent. 



Such a name will have the significance of — 

 Quasi-absolute, symbol Q or Aq. 

 Approximate absolutp, symbol Aa, or aa. 

 Pseudo-absolute, symbol P. 



It should be a short word if possible and 

 suggest a good symbol for its abbreviation. 

 The above list of names is tentative and sug- 

 gestions from others are requested. 



C. F. Marvin 



Weathee Bureau, 

 Oepice of the Chief, 

 Washington, D. C. 



the domestication of the llama 

 To THE Editor of Science : Tor many years 

 one of the favorite arguments of those who 

 wish to prove an immense antiquity for the 

 peoples of the Andean area has been that 

 thousands of years must have gone by before 

 the llama and its kindred, the alpaca, the 

 vicuna, the huanacu, could have been brouglit 



