Aug. 21 '92
Yours of Aug 19 is received. I examined Jupiter last eve & its surroundings & saw nothing but it always accompanied ghost of which there are 2 or 3 kinds. The most usual kind is caused as follows. When you look at Jupiter probably 99/100 of the light enters your eye & depicts in its retina the image of Jupiter but a little of it strikes your eyeball & is reflected to the eye lens & again reflected to the eye which appears when viewing bright objects as a ghost. I am inclined to think this was not the kind that deceived you. Changing eye piece shows that it was not guilty. Had you rotated the objective you would have found I think that the ghost would do the same.
The cause is not clear to me. I well remember how I got deceived when I began to use a telescope on Jupiter. I was certain it was a comet & that it was revolving around the planet & I had Dr. Gould & all the astronomers at Harvard trying to find it. I saw it for 2 or 3 nights & mornings. I then wiped the objective & my comet was gone. I think yours will too. Any way watch it & see what it will turn out to be.
Yours truly Lewis Swift.
|Lewis Swift letter, 1892 Aug 21 (DJVU - low quality) ||87.34 KB|
|Lewis Swift letter, 1892 Aug 21 (DJVU - high quality) ||977.75 KB|