TROWBRIDGE, — SPECTRA AT HIGH TEMPERATURES. 



683 



is pivoted at a point half way between the ruled surface and the slit. In 

 Figure 1, G is the grating, M the point midway between the grating and 

 the slit, C the camera swinging on the arc described from M. Figure 2 

 gives a side view and elevation of the camera. P is the photographic 

 plate, O an opening closed by a slide operated by a lever arm which 

 engages with A. The plate holder closed by another slide S, can move 

 up or down in parallel ways. In Figure 1 is shown a lever arm LM with 

 fulcrum at F. This lever lifts another lever AM, which in turn lifts or 

 closes the shutter A, Figure 2. The lever LM is outside the dark box. 



TijI 



M 



Slit 



and the operation of exposing the plate and closing the camera can be 

 performed without opening the box. The method which Rowland used 

 in mounting the grating is undoubtedly preferable to the above, when 



o 



an accuracy greater than one-tenth of an Angstrom unit is aimed at. 

 The advantage, however, of the method I have employed is in its com- 

 pactness and in the possibility of working in a light room ; moreover, in 



o 



gas spectra an accuracy even to one Angstrom unit is often respectable. 



The capillaries which I used in this investigation may be termed 

 scientific electric furnaces for studying by photography the spectra of 

 gases at high temperatures, and the spectra of the vapor of metals at 

 such temperatures in rarefied media. These capillaries were from four 

 to five inches long, with internal bore of from one millimeter to one 

 and a half millimeters. The metallic terminals were approximately of 



