NIL r.3668. 



Photometers. Hefner Lamp. 



471 



53 659, 53 657. 1 : 23. 



53 668. 1 : 2. 



It is advisable always to obtain 2 comparison lamps of the same sort, keeping one as a chief standard, i 

 and comparing it from time to time with the standard in use. 



53.661. - - idem, calibrated for an accurately prescribed Candle-power in one direction, 

 for working on the photometer bench 



If accurate measurements are desired with these glow lamps -- especially in the photometry 

 of arc light the voltage obtained for the candle-power in question when calibrated must be adhered to. 



53.662. - - idem, calibrated for an accurately prescribed mean horizontal Candle-power, 

 for glow lamp measurements, in accordance with the rules of the Verband Deutscher 

 Elektrotechniker, on Photometer Bench No. 53,657 and with the aid of the Angle Mirror 

 No. 53,658 



53.663. Hefner Lamp, admitted for test by the Physikalisch-Technische Eeichsanstalt (Ztschr. 

 fur Instrumentenkunde, 13, p. 257), with optical flame measuring apparatus (after 

 Kriiss), check gauge and scissors 



53.664. - - idem, verified 



53.665. - - with flame meter after v. Hefner- Alteneck, check gauge and scissors 



s. a. 



0. 5.0 



0. 7.0 



2. 2.0 



2. 6.0 



2. 2.0 



53.666. - - i d e m, verified I 2. 6. 



53.667. - - with 2 flame measuring apparatus, check gauge and scissors, cf. Fig. 53,668 . 2. 10. 



53.668. - - i d e m, verified, Figure 2. 16. 



Cl. 4500, 1221. 



