Letters: Ray Bullock, March 13, 2015

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D Lowe asks (Letters, March 3) why there is blue glass and not green in the signal on the sand line in Lynn.

The reason is that in those old-fashioned signals they have oil lamps (paraffin) which give off a yellow light which, when goes through a blue glass, gives out a green light which is sharper than a natural green and can thus be seen from a greater distance.

Ray Bullock,

ex-M&GNR fireman, Meadow Way, West Lynn