Silverton,
Jan. 31, 1888.
Dear Bly,—
I thought I would send a sketch of the eclipse Annie and I stayed up to see. We had a very beautiful, clear night, not a cloud to be seen. The moon entered its eastern edge into the Penumbra at 8.29 and into the dark shadow at 9.30; and at 11 p.m. the moon was in the centre of the shadow or totally eclipsed, but we could still see it appearing like a large orange and we could see all the principal craters and mountains through the shadow, and I was very interested to watch the stars disappear one after another behind the edge of the moon. Of course I have not shown the sun in the sketch because there is not room, but you must imagine the sun to be about the size of a round table a good distance away to the left of the earth.
Now I will try and explain to you what the Penumbra is and how it is produced. It is produced simply because the sun is so much larger than the earth, and you can make a little experiment and show Freddy and William how it is done. Place two lighted candles or lamps about the width of this paper apart which will represent the sun, then a little way off on a white cloth on the table place a teacup upside down which will do very well to represent the earth, then you will have the black shadow of the Penumbra or half shadow on each side of it. A sixpence will represent the moon, which you can slide gradually across the shadows, and you will have the eclipse to a "t."
It is necessary to have two candles or lamps because the sun is so much greater than the earth and the two candles' light combined represents the sun's light. A small orange perhaps would represent the earth as well or better than a teacup, because the shadow of a cup would not run out to a sharp point, but that of an orange would. That would not matter much either way, only Freddy would most likely be asking the question and you would not be able to answer him.
Your affectionate
Dad.
