312 



or monochromatic glasses, it is simply au incMudescent 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 temperatui-e 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 Fery spiral pyrometer or any other similar instrument. 



Fig. 7. 



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. 



