Franz Schmidt & Haenscli, Berlin S. 79 



III. L. Weber's Photometer with Polarizing Apparatus. 



The instrument is particularly adapted for measuring 1 the brightness 

 of the sky, the c\ouds, the relative distribution of the brightness of the- 

 sky etc. 



IV. Photometer Bench. 



It consists of a cast iron frame with 5 elevation screws, 2 rails of drawn 

 steel tubing, one of which is throughout divided in millimeters, the other 

 according to standard candle units. 3 waggons provided with pointers run upon 

 these rails and are fitted with rack and pinion movement and clamping screws- 

 for accurately adjusting the height of the various luminants. The bed is made- 

 of any required length. As a rule the available length is 250 cm. A completely 

 equipped specimen 150 cm in length is shown at the Exhibition. 



For this photometer bed 2 heads are supplied constructed according 

 to Lummer's and Brodhuri's directions, viz. 



a. Photometer head for equalized luminosities, 



b. Photometer head for equalized and contrasted light, (fig. 17)1 



Fig. 17. 



Vid. >> Photometric Researches-' by Dr. Lummer and Brodhun in the- 

 Zeitschrift fur Instrument enkunde, 1892 and in Schilling, Journal fur 

 Gasbeleuchtung und Wasserversorgung, 1892, No. 29. 



These appliances, which were originally constructed at the insti- 

 gation of the Imperial Physical and, Technical Institution, are already 

 being largely used by prominent gas and electric light works. 



