tant papers, have been lost or destroyed. We are
therefore ignorant of the result of his researches, which were the first
undertaken by any person for the purpose of scientific inquiry.

From his study of the Lansberg and Rudolphine Tables, Horrox arrived at
the conclusion that a transit of Venus would occur on November 24, 1639.
This transit was for some unaccountable reason overlooked by Kepler, who
predicted one in 1631, and the next not until 1761. The transit of 1631
was not visible in Europe.

We are indebted to Horrox for a description of the transit of 1639--the
first that was ever observed of which there is any record; and were it
not for the accuracy of his calculations, the occurrence of the
phenomenon would have been unperceived, and no history of the
conjunction would have been handed down to posterity. As soon as Horrox
had assured himself of the time when the transit would take place, he
wrote to Crabtree to inform him of the date, and asked him to make
observations with his telescope, and especially to examine the diameter
of the planet, which he thought had been over-estimated. He also
requested him to write to Dr. Foster of Cambridge, and inform him of the
expected event, as it was desirable that the transit should be observed
from several places in consequence of the possibility of failure, owing
to an overcast sky. His letter is dated October 26, 1639. He says: 'My
reason for now writing is to advise you of a remarkable conjunction of
the Sun and Venus on the 24th of November, when there will be a transit.
As such a thing has not happened for many years past, and will not occur
again in this century, I earnestly entreat you to watch attentively with
your telescope in order to observe it as well as you can.

'Notice particularly the diameter of Venus, which is stated by Kepler to
be seven minutes, and by Lansberg to be eleven, but which I believe to
be scarcely greater than one minute.'

In describing the method which he adopted for observing the transit,
Horrox writes as follows: 'Having attentively examined Venus with my
instrument, I described on a sheet of paper a circle, whose diameter was
nearly equal to six inches--the narrowness of the apartment not
permitting me conveniently to use a larger size. I divided the
circumference of this circle into 360 degrees in the usual manner, and
its diameter into thirty equal parts, which gives about as many minutes
as are equivalent to the Sun's apparent