For our New England friends, a note on as msrk of summer seen by Henry David Thoreau:
[A] word Thoreau associates with summer is “coolness”as this excerpt shows: “With or without reason, I find myself associating with the idea of summer a certain cellar-like coolness, resulting from the depth of shadows and the luxuriance of foliage, (327). Similarly, he expresses his grateful feeling to wend his way “to some pure and cool stream and bathe therein”(II: 277) Bathing was an important daily routine or “a religious exercise” nthat Thoreau practiced while he lived by Walden Pond (Walden 88). Likewise, he comments on the waters of the river: “The river has a June look, dark, smooth, reflecting surfaces in shade. The sight of the water is refreshing as suggesting coolness” (IV: 116). We might accordingly say that the coolness of summer is linked with shadiness or umbrageousness and water to bathe in. Thus, the three words we have focused on are closely related to each other. The blitheness reminds us of the sunniness and heat of summer, which make the luxuriant foliage of the trees more appealing, because they provide cool shade.
--So Michiko Ono Nature in her Prime: Thoreau's View of Summer, Kawauchi Review: Comparative Studies in English Language and Culture, 4-5 (2006). An accessible version of the quoted passage is in the NYRB Classics reprint, The Journal: 1837-1861 217 (Damon Searles ed. 2009).