SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 



76 



was sealed in the upper closed end of a large glass tube, and connected 

 to the carbon rod by an iron clamp. The lower end of the carbon rod 

 was fastened to another iron clamp, the two clamps being held in 

 place and insulated from each other by a porcelain rod. Attached to 

 the lower clamp was a long copper wire. Just below the lower clamp, 



Starr's Incandescent Lamp, 1845. 



This consisted of a short carbon pencil operating in the vacuum above 

 a column of mercury. 



the glass tube was narrowed down and had a length of more than 

 30 inches. The tube was then filled with mercury, the bottom of the 

 tube being put into a vessel partly full of mercury. The mercury ran 

 out of the enlarged upper part of the tube, coming to rest in the narrow 

 part of the tube as in a barometer, so that the carbon rod was then in 

 a vacuum. One lamp terminal was the platinum wire extending 

 through the top of the tube, and the other was the mercury. Several 



