Section III, 1921 [95] Trans. R.S.C. 



The Effect of Thermo-liiminescence on Electrical Conductivity 



By C. A. Mackay, M.A. 



Presented by Professor H. L. Bronson, F. R.S.C. 



(Read May Meeting, 1921) 



Our present knowledge of the physical changes which occur 

 during photo- and thermo-lurninescence of solids is very incomplete. 

 In order to arrive at any satisfactory theory as to the nature of this 

 type of luminescence, it is essential that as much data as possible be 

 obtained concerning the variation in the properties of solids when 

 emitting light of this sort. 



On the basis of the commonly accepted theories as to the 

 mechanism of photo-luminescence it might be expected that the 

 electrical conductivity of matter is greater during the emission of 

 light than in its normal state. However, it has been shown by 

 Nichols and Merritt^ that the conductivity of eosin is unchanged 

 when this substance emits fluorescent light, under the action of ultra- 

 violet light. 



It was suggested that the writer investigate the electrical con- 

 ductivity of various substances, which, under suitable conditions, are 

 thermo-luminescent. Three crystals, calcite, fluorite and feldspar, 

 were examined. All showed thermo-luminescence when gently 

 heated over a Bunsen burner. 



Apparatus and Method of Measurement 



The crystals, after being carefully cleaned with pure alcohol, 

 were mounted as shown in Figure 1. The brass electrodes were 

 cemented to the parallel faces of the crystal by means of a metallic 

 preparation named "Smooth-On." 



1 Publication 152, Washington Carnegie Institution. 



