time during the day.
Among the works I had projected was that of rediscussing all the
observations made on the transits of Venus which had occurred in 1761
and 1769, by the light of modern discovery. As I have already remarked,
Hell's observations were among the most important made, if they were
only genuine. So, during my almost daily visits to the observatory, I
asked permission of the director to study Hell's manuscript, which was
deposited in the library of the institution. Permission was freely
given, and for some days I pored over the manuscript. It is a very
common experience in scientific research that a subject which seems
very unpromising when first examined may be found more and more
interesting as one looks further into it. Such was the case here. For
some time there did not seem any possibility of deciding the question
whether the record was genuine. But every time I looked at it some new
point came to light. I compared the pages with Littrow's published
description and was struck by a seeming want of precision, especially
when he spoke of the ink with which the record had been made. Erasers
were doubtless unknown in those days--at least our astronomer had none
on his expedition--so when he found he had written the wrong word he
simply wiped the place off with, perhaps, his finger and wrote what he
wanted to say. In such a case Littrow described the matter as erased
and new matter written. When the ink flowed freely from the quill pen
it was a little dark. Then Littrow said a different kind of ink had
been used, probably after he had got back from his journey. On the
other hand, there was a very singular case in which there had been a
subsequent interlineation in ink of quite a different tint, which
Littrow said nothing about. This seemed so curious that I wrote in my
notes as follows:

"That Littrow, in arraying his proofs of Hell's forgery, should have
failed to dwell upon the obvious difference between this ink and that
with which the alterations were made leads me to suspect a defect in
his sense of color."

The more I studied the description and the manuscript the stronger this
impression became. Then it occurred to me to inquire whether perhaps
such could have been the case. So I asked Director Weiss whether
anything was known as to the normal character of Littrow's power of
distinguishing colors. His answer was prompt and decisive. "Oh yes,
Littrow was color-blind to red. He could not distinguish b