532 



KINETICS OF BIOLUMINESCENT REACTION. I 



have used at ^ a special tungsten wire lamp kindly loaned to me by 

 the Nela Research Laboratories. The lamp has a filament made of a 

 single loop of tungsten wire whose diameter is 0.2 mm. An image of a 

 small vertical portion of this filament is focussed by a lens, B, upon the 

 filament of a smaller pyrometer lamp, C, enclosed in a housing, and 

 the image of both filaments is then viewed through a telescope at D. 

 Both lamps are run from storage cells, the amperage being controlled 

 by variable resistances. The intensity of the larger or background 

 lamp is held at a constant value by continual observation of an am- 

 meter in the circuit. The current through the pyrometer lamp is 

 read from a milammeter in this circuit. The relation between inten- 

 sity of Hght in the pyrometer filament and the current producing it 

 is determined by reducing the intensity of the constant background 

 by the interposition of various screens or similar devices of known 



Fig. 3. The optical pyrometer. A, background lamp; B, objective lens; C, 

 pyrometer lamp; D, telescope; E, film; F andG, diaphragms; F, monochromatic 

 filter. 



transmission values. For this purpose I have used the set of sector 

 discs made by the Leeds and Northrup Company. These discs 

 have transmission values of 80, 70, 60, and 50 per cent. At my 

 request the manufacturers made a fifth special disc with a transmis- 

 sion value of 55 per cent. By these discs and combinations of them 

 it is possible to reduce the light to the following percentages of the 

 original value, 80, 70, 60, 55, 50, 35, 30, 25, 20, 15, 10, 5. By reducing 

 the background current two overlapping series of readings connecting 

 the brightness of the pyrometer filament with the current producing 

 that brightness are obtained, extending the range of the calibration 

 to lower transmission values. In each case a disc is rapidly revolved 

 between the background and pyrometer lamp, and the current through 

 the latter is adjusted until the brightness of its filament matches that 



