Lighthouse lens

Each night I like to look out of the bedroom window to watch the flashing light on the distant island of Inchkeith where a lighthouse has been since 1803 to warn ships approaching Leith and other ports of the Forth.
The lighthouse lens here at the museum in Edinburgh came from Inchkeith where it was installed in 1889 and replaced in 1985. The small light inside would be magnified to give off a light equivalent to 167,000 candles and visible for 21 miles with the revolving light showing a flash every half minute and making a complete revolution in four minutes.
The lens was made up of 8 sections and as the light lined up with each the flash was sent out. Prisms close together but not connected, sent it out horizontally over the water. Surrounding all this were long panes of glass which had to be spotless every evening. During good weather the prisms and mantle were protected by blinds because the sun glinting through the glass and on to the prisms could have had a burning effect.
British lighthouses today are automatic and controlled by computer but still flash their warning light to warn of hazards. Mariners safely plot their course now with GPS but they can still navigate using each lighthouse’s own distinguishing building features and light sequences.