NO. 5 



HYDROGEN CYANIDE BRACKETT AND LIDDEL 



EXPERIMENTAL RESULTS 



The results to be presented here were obtained with an automatic 

 recording apparatus yielding high resolution and possessing certain 

 novel features. An earlier self-recording instrument of high resolution 

 was set up at the University of California by F. S. Brackett, yieid- 

 ing on effective slit-width of lo A. A similar instrument, but one 

 with considerably greater aperture, was constructed by E. D. McAlis- 

 ter at the University of Oregon, yielding an effective slit-width of 

 6 A. The instrument used in the present investigation at the Fixed 

 Nitrogen Laboratory is of approximately the same aperture, though 

 of considerably greater focal length, and yields the same eff'ective 

 resolution. 



Coffirnsfing MiTor 



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Fig. I. — Diagrammatic sketch of spectrograph. 



The instrument is of the Littrow form, wherein the light twice 

 traverses two 60° prisms. The aperture is limited by the smaller of 

 the two prisms, whose face is 20 cm. high and 15 cm. basal width. 

 The instrument is used at a focal length of 2 meters. The body, 

 a large casting, may be sufficiently evacuated to remove atmospheric 

 absorption. Wave length variation is accomplished by rotation of 

 the plane mirror, which is coupled with the motion of the photographic 

 plate by a lever system. The use of a mechanical lever system with a 

 variable pivot permits a wide range of variation of relative motion of 

 the plate carriage to the angular rotation of the mirror, giving prac- 

 tically any desired spread of spectrum. This improved mechanical 

 system, together with the use of photographic plates instead of film 

 or paper, gives a much greater reproducibility of spectrum and 

 accuracy of wave length than heretofore obtained. The calibration 

 was effected with mercury arc spectra and water vapor bands, the 



