Phosphorescence and Colour by Electricity. 269 



and intense azure blue tints. The phosphorescence of these 

 specimens had light and colour of exquisite delicacy. 



Chalk gave an orange light, rather dull, when heated in its 

 natural state ; but if made red hot, allowed to cool, and then 

 twelve times electrified, it evolved a bright orange light when 

 heated. 



Common egg-shells gave no light ; but twelve discharges of 

 the electrical jar conferred a bright purple light. 



The preceding experiments were made with substances which 

 did not possess this peculiarity in their ordinary state, yet exhi- 

 bited the conferred phenomena, with such beauty, variety, and 

 intensity of colour, as to surpass very many natural specimens. 



The results obtained with such varieties of fluor spars as I 

 had access to, appeared in a tabular form in my preceding 

 communication ; the examination of other specimens presented 

 similar effects. 



The probable localities of the following varieties of fluors 

 have been assigned by Mr. Sowerby : 



[The natural phosphorescence is shown in the second column ; the third column 

 states the number of explosions sustained by the calcined mineral, and also the 

 phosphorescent appearances by heat subsequently applied.] 



16 to 12, a bright green, ending 

 with purple. 

 36. The green is increased nearly 

 to the intensity of the natural 

 phosphorescence of chloro- 

 phane. 



2 ' S35fe f *> 40. First,,,*, A 



from Wear-dale f^W blue and P w 'P le ' \ Vlolet and sh ' OH 3 P u 

 Cumberland ...... J I ver y Beautiful. 



3. Pale 



ale yellow cubic). . .. .... J12, 24 36. Yellowish light of 



fluor (Gersdorfl") I Green and uio/e/ light. .< short duration, terminating 



[ with purple. 



ubic fluor (palel f . ,. . [12. Green and rich purple lidit- 



green) from Cum- \ Ll f li ? en > changing I 24 Grem and ric h/,r,>/e light, 

 berland ......... J to V ink d molet ' ' ' \ ending with orange colour^ 



j f!2. Green and rich purple light. 



>Rich purple .......... < 36. Green light and other tints, 



[ rapidly changing. 



5. Cubic fluor (pale 

 green) Cumberland 



most white. 



12. A fragment emitted intense 

 light, pale greenish tint, al- 



50. Intensely rich green liyht of 

 short duration. 



7. Crystalline massive ( Dull green and pink, of V, , Yellou>i<h llnht 

 fluor, Derbyshire. . \ short duration ...... T 4 ' J 



VOL. I. F EIJ . 1831. T 



