512 



SCIENCE PROGRESS 



thermometers may be 2 inches or 6 feet long, 0*2 to 2 inches 

 in diameter, their scale may embrace only J° C. in all, or 

 700° C, may be divided so that i mm. = "oi°C. or io°C., may 

 be intended for an immersion of two inches or five feet ; hence 

 apparatus of the greatest variety is necessary for these alone, 

 and in almost all forms of instruments similar wide variations 

 of pattern have to be arranged for. For thermometer standard- 

 isation a series of baths is provided, in which are stirred liquids 

 heated electrically, available for temperatures up to 700° C. 

 For thermo-couple, resistance, radiation and optical pyrometers 

 electric furnaces of very varied types have been designed, those 

 for moderate temperatures up to 1,400° C. being wound with 

 nickel or platinum. Above that point special forms of electric 

 furnace are used, in which the resistor is made of carbon or 

 graphite. In these furnaces controllable steady temperatures 

 up to about 3,000" C, uniform over considerable areas, may be 

 obtained, while for attainment of the highest terrestrial 

 temperatures arc-furnaces are employed. 



The following is a table of the values of a number of fixed 

 points employed in pyrometric work : 



