or monochromatic glasses. It is simply an incandescent electric lamp in a 
black tube and it is operated and calibrated in a similar manner to the 
Holborn instrument. 
While there are a number of instruments, more or less reliable, which 
may be bought from scientific shops, the above list represents the ones in 
most common use. In the opinion of the author it is neither necessary nor 
advisable to equip a high temperature laboratory with an elaborate outlay 
‘of expensive commercial apparatus. The object of such a laboratory should 
be to teach the student the fundamental principles of the subject, the appli- 
cation and limitations of these principles to commercial instruments and to 
train the student in the use of a few types of instruments. After having 
mastered the principles of radiation pyrometry the student will have 
no difficulty in making a temperature observation by means of a direct 
reading Féry spiral pyrometer or any other similar instrument. 
Wray “1. 
For the purposes of calibration or standardization of instruments the 
laborator should also include a boiling point apparatus for each of the 
fixed points, or if the fusion temperatures of the metals are used, a melting 
furnace. 
