“Thoughts shut up want air,
And spoil, like bales unopen’d to the sun.”

“Come On In”, p. 88
The Journey Home (1977)

As quoted in Simpson's Contemporary Quotations‎ (1988) by James Beasley Simpson, p. 211

Another handwriten message on Elvis' King James -Bible http://www.dailymail.co.uk/news/article-2188891/Elvis-bible-containing-handwritten-notes-star-expected-fetch-thousands-auction.html
Variant: Truth is like the sun. You can shut it out for a time, but it ain't going away.

"Letter to Joseph Priestley" in response to Priestley's "experiments on the restoration of air [by plants] made noxious by animals breathing it, or putrefying it..." read in Philosophical Transactions LXII 147-267 of the Royal Society (1772) and quoted in John Towill Rutt, Life and Correspondence of Joseph Priestley http://books.google.com/books?id=psMGAAAAQAAJ... Vol.1 (1831).
Context: That the vegetable creation should restore the air which is spoiled by the animal part of it, looks like a rational system, and seems to be of a piece with the rest. Thus fire purifies water all the world over. It purifies it by distillation, when it raises it in vapours, and lets it fall in rain; and farther still by filtration, when keeping it fluid, it suffers that rain to percolate the earth. We knew before that putrid animal substances were converted into sweet vegetables when mixed with the earth and applied as manure; and now, it seems, that the same putrid substances, mixed with the air, have a similar effect. The strong, thriving state of your mint, in putrid air, seems to show that the air is mended by taking something from it, and not by adding to it. I hope this will give some check to the rage of destroying trees that grow near houses, which has accompanied our late improvements in gardening, from an opinion of their being unwholesome. I am certain, from long observation, that there is nothing unhealthy in the air of woods; for we Americans have everywhere our country habitations in the midst of woods, and no people on earth enjoy better health or are more prolific.

Cemetery World (1973)
Context: The sun was setting, throwing a fog-like dusk across the stream and trees, and there was a coolness in the air. It was time, I knew, to be getting back to camp. But I did not want to move. For I had the feeling that this was a place, once seen, that could not be seen again. If I left and then came back, it would not be the same; no matter how many times I might return to this particular spot the place and feeling would never be the same, something would be lost or something would be added, and there never would exist again, through all eternity, all the integrated factors that made it what it was in this magic moment.

Source: High Windows

Source: Down and out in Paris and London (1933), Ch. 27, on the morning after Orwell is let out of his first tramps' accommodation, or 'spike'.