What is the peculiarity of the Indian summer?

November 19.

Up river in boat to Hubbard's meadow, cranberrying. They redden all the lee shore, the water being still apparently at the same level with the 16th. 

This is a very pleasant and warm Indian-summer afternoon. Methinks we have not had one like it since October. 

November 19, 2023

This, too, is a gossamer day, though it is not particularly calm. My boat I find to be covered with spiders, whose fine lines soon stretch from side to side. 

Got a bushel and a half of cranberries, mixed with chaff.

What is the peculiarity of the Indian summer? From the 14th to the 21st October inclusive, this year, was perfect Indian summer; and this day the next?

Methinks that any particularly pleasant and warmer weather after the middle of October is thus called. Has it not fine, calm spring days answering to it?

H. D. Thoreau, Journal, November 19, 1853

This, too, is a gossamer day, though it is not particularly calm. See ? November 1, 1851("Why should this day be so distinguished?"), November 3, 1857 ("I see against the sunlight, where the twigs of a maple and black birch intermingle, a little gossamer or fine cobwebs, but much more the twigs, especially of the birch, waving slightly, reflect the light like cobwebs. It is a phenomenon peculiar to this season, when the twigs are bare and the air is clear."); November 15, 1858 ("Gossamer, methinks, belongs to the latter part of October and first part of November"). See also November 3, 1853 ("There are very few phenomena which can be described indifferently as occurring at different seasons of the year")  See also A Book of the Seasons, by Henry Thoreau, Gossamer Days

What is the peculiarity of the Indian summer?  October 14, 1859 ("A fine Indian-summer day. The 6th and 10th were quite cool, and any particularly warm days since may be called Indian summer (?), I think");. October 31, 1858 (" It is a fine day, Indian-summer-like, and there is considerable gossamer on the causeway and blowing from all trees. That warm weather of the 19th and 20th was, methinks, the same sort of weather with the most pleasant in November (which last alone some allow to be Indian summer)."); See also A Book of the Seasons, by Henry Thoreau, Indian Summer

My boat I find to be covered with spiders, whose fine lines soon stretch from side to side. See October 20, 1856 ("I think that all spiders can walk on water, for when, last summer, I knocked one off my boat by chance, he ran swiftly back to the boat and climbed up, as if more to avoid the fishes than the water.”)  See also A Book of the Seasons, by Henry Thoreau, Gossamer Days