Front. SEMAPHORE PAT US FEB 20 CAN MAR 29 APL 13 ENG 24 1877 ( 3 1/2 in cartouche )
This is a nice old solid RED color glass lens. actual measurement is 5 inches .
selenium
yet one more story of interest is the history of development in signal glasses
standardisation of color and signal oils for their use.and Dr Mortimer frank. testing of the colored blind at distances and how flashed glass compaired to glass with solid color Railroad Gazette vol 37 pg 141 1904.
and another interesting article The Engineer vol 27-28 pg 118 1894
Front. SEMAPHORE PAT US FEB 20 CAN MAR 29 APL 13 ENG 24 1877 ( 3 1/2 in cartouche )
This is a nice old solid RED color glass lens. actual measurement is 5 inches .
selenium
yet one more story of interest is the history of development in signal glasses
standardisation of color and signal oils for their use.and Dr Mortimer frank. testing of the colored blind at distances and how flashed glass compaired to glass with solid color Railroad Gazette vol 37 pg 141 1904.
and another interesting article The Engineer vol 27-28 pg 118 1894