330 RECORDS. 



Mr. Levison presented the following note on a Tribo- 

 phosphoroscope : 



Discs of thick pasteboard about I 5 cm. in diameter are evenl)^ 

 sanded on one or both sides on a coating of liquid glue with 

 the materials to be examined in powder, narrow bands being- 

 sufficient and only small quantities of the materials required. 



The disc selected is then rotated at a known and usually 

 moderate speed (twelve revolutions per second, for example) by 

 any convenient mechanism, such as an ordinary rotator used for 

 illustrating the recomposition of light. 



A point or brush of wire or other material, or a piece of the 

 same material with w^hich the disc is coated, being pressed 

 against the sanded surface, produces a trail of light which ex- 

 tends from the point of contact in an arc more or less around 

 the disc ; varying in color with different materials and in length 

 with the speed, and is maintained for some time unless the 

 material is rubbed off by extreme friction. A grindstone or 

 corundum wheel may often be used to advantage with hard 

 substances as a substitute for the disc, since a specimen held 

 against it soon coats it with a trace of the material which shows 

 its luminous trail beautifully. 



By means of the device described, the intensity of the light 

 may be determined with a photometer, its duration from the 

 length of the trail, and its spectrum delineated with a spectro- 

 scope. 



The following approximate tentative results of the examina- 

 tion of a few minerals are given to illustrate its applicability. 



I. Sphalerite (i) from Utah. Light yellow concretions in 

 gray massive sphalerite. Visible trails of a yellow orange color 

 of respectively increasing brilliancy and length are produced 

 with the tip of the finger ; a wooden match ; the finger nail ; a 

 brass wire brush ; and a steel wire brush, or point ; visible, with 

 the latter, at a distance of several yards and extending about 

 one quarter around the disc at the above speed. Hence, the 

 duration is about 0.02 s. The spectrum is short, extending" 

 from about the line C to the line £ and embracing some red, 

 orange, yellow, yellow-green and green. (2) From another 



