NO. 12 



SPECTROBIOLOGY BRACKETT AND McALISTER 



avoiding the difficulty of correcting for window transmission. Only 

 two settings of collimator and camera have been required for the 

 recording of the entire range of the spectrum, the region from 2,500 A. 

 to 3,900 A. being traversed at one setting and the region from 

 3,900 A. to i./jji at the other. In this case a small spread or high 

 gear ratio has been used in recording to show conveniently the entire 

 spectrum. 



Figure 3 is another automatic record of the mercury arc taken with 

 a vacuum thermocouple of the type described by Brackett and Mc- 

 Alister.^ As will be seen this record has been taken with a finer slit- 

 width, the spectral range subtended by the slit being of the order of 



I I I 



3200 3300 3400 



Fig. 3. — Record of mercury spectrum taken with vacuum thermocouple 

 showing higher resolution and greater stability. 



8 A. Here a lower gear ratio has been used in order to secure a larger 

 spread. This permits the ready integration of areas for quantitative 

 comparisons. One will note that the same order of deflection has been 

 achieved despite the great increase in resolution and improvement in 

 stability of zero. 



Plate 3, Figure i, shows a photographic spectrogram of the quartz 

 mercury arc. Although rather a wide slit has been used it will be 

 seen that the finer lines are sharply defined. Furthermore, although 

 over 4 cm of slit-length has been shown in the illustration excellent 

 straightness of line has been obtained. 



Plate 3, Figure 2, shows a typical spectrogram obtained with bio- 

 logical material where the organisms are destroyed by the wave lengths 

 of a given spectral region. This was obtained by Doctor Meier, using 

 unicellular algae, and was discussed in her paper " The Lethal Action 



^The automatic recording of the infra-red at high resolution. Rev. Sci. In- 

 struments, vol. I, no. 3, pp. 181-193, 1930. 



