140 THE TANTALUM LAMP. 



further be noticed that even afterwards the resistance of tantalum 

 goes on rising, while the resistance of carbon keeps dropping. 

 Therefore the increase or decrease of pressure causes the strength of 

 current, and with it the illuminating value, to rise or fall at a quicker 

 rate in the carbon lamp than in the tantalum lamp, and, consequently, 

 the latter is less sensitive to variations of pressure than the former. • 

 Having thus related the whole history of the development of the 

 tantalum lamp and fully entered into a critical comparison between 

 it and the carbon filament lamp, we need scarcely add that we do 

 not intend, of course, to be satisfied with what we have already 

 obtained. For the time being, however, and until a larger building 

 has been erected for the production of tantalum, our firm has resolved 

 to keep to the type for which there is an immediate practical demand. 

 That is the lamp for 100 to 120 volts, which supplies 25 Hefner 

 candlepower at 110 volts, or will have a higher or lower illuminat- 

 ing value if worked at correspondingly higher or lower voltages. In 

 conclusion, I w^ould recapitulate the properties which we claim as 

 peculiar characteristics of our invention as follows : 



1. The tantalum lamp has a filament made of a metallic conduc- 

 tor, and burns at once on being connected without any previous 

 heating. 



2. The light-giving wire is prepared by melting in a vacuum and 

 drawing. It is tough even in the cold state, and can therefore be 

 coiled and fixed in the lamp when cold. 



3. A relatively great length of wire can be placed in a sim2)le man- 

 ner within a bulb of ordinary dimensions. 



4. Tantalum ore exists in considerable ({uantities and can be easily 

 procured. 



5. Similar principles of treatment can be adhibited to other metals 

 of a very high melting point. 



