the only one. Yet, to my eyes, all the seeming corrections
in the journal were of the most innocent and commonplace kind,--such
as any one may make in writing.

Then I began to compare the manuscript, page after page, with
Littrow's printed description. It struck me as very curious that
where the manuscript had been merely retouched with ink which was
obviously the same as that used in the original writing, but looked
a little darker than the original, Littrow described the ink as of
a different color. In contrast with this, there was an important
interlineation, which was evidently made with a different kind of
ink, one that had almost a blue tinge by comparison; but in the
description he makes no mention of this plain difference. I thought
this 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."

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 between the color of
Aldebaran and that of the whitest star." No further research was
necessary. For half a century the astronomical world had based an
impression on the innocent but mistaken evidence of a color-blind
man respecting the tints of ink in a manuscript.

About the middle of the nineteenth century other methods of measuring
the sun's distance began to be developed which, it was quite possible,
might prove as good as the observation in question. But the relative
value of these methods and of transits of Venus was a subject on which
little light could be thrown; and the rarity of the latter phenomena
naturally excited universal interest, both among the astronomers
and among the public. For the purpose in question it was necessary
to send expeditions to different and distant parts of the globe,
because the result had to depend upon the times of the phases,
as seen from widely separated stations.

In 1869 the question what stations should be occupied and what
observations should be made was becoming the subject of discussion
in Europe, and especially in England. But our