If photographs are one of the candles by which we read history, a blaze of light will be shone on the past from Friday at the British Library. Here a vast exhibition of 19th-century photography will give the public a taster for the first time of the extent of the library’s photographic treasures, which amount to nearly half a million images. Culled from these, 200 items will reveal a breadth of material from the dawn of photography to the present day, hinting at a collection so large that it seems extraordinary that it has remained in obscurity all this time. READ ON.