RECENT PROGRESS IN PHYSICAL SCIENCE. 113 
gas-thermometer scale is given with very considerable accu¬ 
racy by a simple parabolic curve. Since this curve must of 
necessity pass through the freezing and boiling points of 
water, the whole curve becomes established when the resist¬ 
ance of the thermometer is measured at one additional fixed 
point. If observations are to be made at high temperatures, 
the boiling point of sulphur (445° C.) is a convenient sec¬ 
ondary point. For very low temperatures the boiling point 
of oxygen, for example, may be employed. 
The extremely wide range over which one and the same 
instrument may be used commends the platinum thermom¬ 
eter as a convenient working instrument above all others. 
At the meeting of the British Association in 1899 propo¬ 
sals were submitted by Professor Callendar for the adoption 
of the platinum resistance thermometer as a practical stand¬ 
ard of reference for scientific research. 
The following resolutions, taken from the text of the pro¬ 
posals, embody the suggestions offered for the adoption of 
the new scale of temperature: * 
u (1.) That a particular sample of platinum wire be selected, and plati¬ 
num resistance thermometers constructed to serve as standards of the 
platinum scale of temperature. 
“ (Note. —A degree centigrade of temperature on the scale of a platinum 
resistance-thermometer corresponds to an increase of resistance equal to 
the hundredth part of the change of resistance between 0 and 100 0. In 
other words, temperature pt on the platinum scale is defined by the 
formula: 
pt = 100 (. R-R 0 )/(R'-R 0 ), 
in which the letters R , R 0 , and R / stand for the resistances of the 
thermometer at the temperatures pt, 0, and 100 O., respectively. The 
melting point of ice is taken as the zero of this scale, in accordance with 
common usage.) 
“ (2.) That the scale of temperature t deduced from the standard plati¬ 
num scale by means of the parabolic difference formula : 
t—pt = d{tf 100 — 1) ^ /100, 
which has been proved to give a very close approximation to the true 
or thermodynamic scale, be recommended for adoption as a practical 
standard of reference, and be called the British Association Scale of 
Temperature. 
Phil. Mag. (5), vol. 48, Dec., 1899, p. 520. 
