642 Transactions of the American Institute. 



from the solid to the gaseous state. This passing of particles of car- 

 bon from the gaseous to the solid state, and back to the gaseous state, 

 a great many million times per second, sets the ether in vibration and 

 produces light. 



Dr. P. II. Yan der Weyde — I indorse that fully ; although I had not 

 the pleasure of hearing it when stated here before. I would like to 

 ask why it is that light is not produced when we mix the gas with 

 air, as we do in the Bun sen burner, where the heat is greater. 



The President — For the reason that the mixture checks the change, 

 and the lower rate of vibration produces heat but no light. 



Mr. J. K. Fisher — In burning hydrogen, magnesia or any powder 

 dropped into the flame makes it luminous. How do you explain that 

 upon your theory ? Is carbon an exception ? 4 



The President — The calcium light is produced by burning hydro- 

 gen by a jet of oxygen, and placing a piece of lime at the point of 

 combustion. The intense heat sets the particles of lime into a higher 

 state of vibration, in like manner as overtones are produced by musical 

 sounds. That light would not be produced in any ordinary flame. 

 The particles of a powder in a flame being luminous, is a result very 

 different from that which produces the light we have here to-night. 



Dr. Van der Weyde — I think the theory of the President agrees 

 perfectly with the facts. We must remember that heat is a vibration. 

 If the vibration becomes rapid enough to be perceptible to the eye, 

 we call it light ; below that, we call it'heat. In order to be luminous, 

 the vibrations must be 400,000,000,000 in a second ; and it goes up 

 to about 700,000,000,000. Below 400,000,000,000, it is invisible, 

 but is felt as heat. Above a little more than 700,000,000,000, it is 

 invisible, but is made manifest in photography. These rapid alter- 

 nations between the gaseous and the solid state — for, although each 

 particle goes through the process but once, there are millions of 

 millions of particles constantly changing — increase the velocity of 

 the heat vibrations, and make them luminous. 



A Member — In using the Bunsen burner, stop the holes through 

 which the air has access, and you produce the ordinary bright blaze, 

 and it will smoke a paper held over it, showing the presence of solid 

 carbon. Allow the air to mix with the gas, and when it is thoroughly 

 hot, there is no solid carbon at all, and no light. How is that 

 explained by the vibration theory % 



Dr. Van der Weyde — The greater the heat, the more of the lesa 

 rapid vibrations there will be. 



Dr. D. D. Parmelee — We produce the electric light from solid 



