I’ve just discovered Google’s Ngram, which is fun to play with. It will search for words and phrases within a million scanned books. This is what it did with “prehistory” and “Stonehenge”. “Prehistoric” first appeared in print in English in 1851, and you can see a steady spread here of the use of “prehistory”. (If you graph “prehistoric”, the rise is even more dramatic, starting in 1860 and reaching a plateau around 1920, but it dwarfs the Stonehenge graph into a low wobble – these lines express the relative use of words to the entire lexicon, and are said to be most reliable between 1800 and 2000.)
Stonehenge has a more interesting graph. I’d guess the 1810s peak is connected to the excavations around Stonehenge in the early 19th century, not least by people like Cunnington and Colt Hoare. The 60s peak would fit the huge interest generated first by Richard Atkinson (his Stonehenge came out in 1956 and was paperbacked by Penguin in 1960) and then Gerald Hawkins (Stonehenge Decoded was first published in 1965).
But what’s that peak in the 1870s? Petrie? Darwin? A surge in visitors after the London train reached Salisbury in 1857? (But if that, why was it slow to start and did it then fall off?) Any ideas?