I have a little shadow that goes in and out with me...

...And what can be the use of him is more than I can see.
He is very, very like me from the heels up to the head,
And I see him jump before me, when I jump into my bed.

Well, I could type out the rest of the poem, my mom made me memorize it when I was a child, but poetry is exactly not the point here.

I'm reading Roberto Casati's The Shadow Club: The Greatest Mystery in the Universe--Shadows--and the Thinkers Who Unlocked Their Secrets. What an awkward subtitle. I've started the book a couple of times, but I've never gotten past page 14 or 15 because every time I read them, I need to take a break and think, "Wow," for awhile. Then I have to start the book over.

Casati is making a very basic point, that shadows and light play a large role in the history of modern science. He runs through the history of the lightbulb pretty quickly, Edison's incandescent bulb, etc. But I'm always blown away by the implications of his next point--that with the introduction of the filament lightbulb, not only did concept of light change, so did the concept of shadows. For the first time in history, both light and shadows were *stable*. That seems kind of obvious, but imagine how much the average person's worldview must have changed. Always before, even with gas lamps, shadows moved. They flickered if caused by artificial light, and they moved across the ground w/time if caused by natural light. Suddenly we have the capability of producing shadows that don't move.

Modern shadows are completely different than ancient shadows, and that is very cool. I can't believe I hadn't noticed it before this.

Actually, I guess poetry is the point, because Robert Louis Stevenson captured the essence of change when describing his childhood companion.

I have a little shadow that goes in and out with me,
And what can be the use of him is more than I can see.
He is very, very like me from the heels up to the head;
And I see him jump before me, when I jump into my bed.

The funniest thing about him is the way he likes to grow--
Not at all like proper children, which is always very slow;
For he sometimes shoots up taller like an india-rubber ball,
And he sometimes goes so little that there's none of him at all.

He hasn't got a notion of how children ought to play,
And can only make a fool of me in every sort of way.
He stays so close behind me, he's a coward you can see;
I'd think shame to stick to nursie as that shadow sticks to me!

One morning, very early, before the sun was up,
I rose and found the shining dew on every buttercup;
But my lazy little shadow, like an arrant sleepy-head,
Had stayed at home behind me and was fast asleep in bed.