10 Mr. G-. A. Hemsalech on the Relative Behaviour 



point a series of experiments were made, of which one may- 

 be mentioned here. Aflat explosion surface was obtained by 

 means of burner No. 1 and placed in the optic axis of the 

 collimator (fig. 4). A metal screen was fixed in front o£ 



l ■ .' I I I Explosion region. 

 Optic axis, r ^L Burner 



Method of observing spectrum of explosion region. 



the flame in such a way that only light from the explosion 

 region could pass along the axis. It is true that a thin 

 stratum of flame remained at the end of the explosion sur- 

 face, but it was small compared with the depth of the latter, 

 and, if no flame lines were emitted by the explosion region, 

 their intensities should appear appreciably reduced relative 

 to the cone lines. But the resulting photographs show no 

 indication whatever of a relative weakening of the flame 

 lines. 



Similar results were obtained with other burners by ex- 

 amining the explosion region near the base of the cones. 

 We must therefore conclude that the emission of flame lines 

 is already initiated during the passage of the material 

 through the thin film of the explosion region. This was 

 further corroborated by some of my later photographs, 

 which show a slight intensification of these lines in the cone 

 region. 



Cone lines emitted by flame. 

 The superior definition of the image of the flame on the 

 slit due to the new type of burner used, and also to the 

 excellent correction of the Zeiss projection-objective, has 

 brought out an interesting and important new fact, which 

 had not been observed in our previous experiments — namely, 

 that many of the lines formerly included in our class of 

 fundamental lines occupy in reality a position intermediate 

 between these and the lines of the supplementary spectrum. 

 They are cone lines in the sense that they are strongly 

 emitted by the cone, but only feebly emitted by the flame. 



