Last night I dreamed about mercury — huge, shining globules of quicksilver rising and falling. Mercury is element number 80, and my dream is a reminder that on Tuesday, I will be 80 myself.

Elements and birthdays have been intertwined for me since boyhood, when I learned about atomic numbers. At 11, I could say “I am sodium” (Element 11), and now at 79, I am gold. A few years ago, when I gave a friend a bottle of mercury for his 80th birthday — a special bottle that could neither leak nor break — he gave me a peculiar look, but later sent me a charming letter in which he joked, “I take a little every morning for my health.”

Eighty! I can hardly believe it. I often feel that life is about to begin, only to realize it is almost over. My mother was the 16th of 18 children; I was the youngest of her four sons, and almost the youngest of the vast cousinhood on her side of the family. I was always the youngest boy in my class at high school. I have retained this feeling of being the youngest, even though now I am almost the oldest person I know.

Oliver Sacks wrote an opinion piece for The New York Times about turning 80. Today is his birthday.

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