BAIRD &TATLOCK (LONDON) LTD. 



PHOTOMETER HEADS, STANDARDS OF LIGHT, LAMP ROTATORS, ETC. 



4820 



4820 T Disc Box only for use with grease spot or star disc . . 

 482 1 T Spare Bunsen or Leeson Star Discs 



4824 



3 3 ( 



per box of 12 12 < 



4822 T Carrier for above on rollers, arranged for bar or standard section shown above with pointer 1 12 < 

 4823 T Simmance-Abady Patent Flicker Photometer. Head for angle and horizontal testing 10 10 



4824 T Ditto, for horizontal testing only . . . . . . . . . . . . ..55 



The principle of this is quite a novel one, and replaces the grease spot and similar devices familiar to all 

 experimentalists. By its means light of any colour can be compared with any known standard of light. It 

 is in fact the solution of the " colour difficulty " which has hitherto pressed so hardly on photometrists, especially 

 with modern forms of lighting, &uch as arcs, metallic filaments, incandescent mantles, etc. When the lights are 

 unequal, a flickering effect is present, but when equality is obtained, all that is seen is an apparently motionless 

 disc. With this photometer the " personal error " is avoided, even with the greatest contrast between the lights. 



4825 T Spare Sighting Wheels for Flicker Photometers Nos. 4823 and 4824 . . . . 07 



CROSS STRET HATTO^T GARDETST, E- C 



