ASTRONOMY IN WANSTEAD.
159
the disc of the planet," "Observations made with Mr. Hadley's
reflecting Telescope," etc., etc., may be found in the Phil. Trans.,
vols. xxix. to xxxii.
His collections cf Natural History were presented to the
Ashmolean Museum, Oxford.
After the death of Dr. Pound, his widow left the rectory,
removing to a small house on her brother's estate, The Grove. The
house adjoined the stables, and was just behind the Clock House
(Capt. Kindersley's).
Here, when free from his studies at Oxford, Dr. Bradley resided,
and "observed at his Aunt Pound's house in Wanstead Town,"
beginning in July, 1725. He tells us "the house was small, the
ground room only 71/2 feet high, with a loft or garret over it."
It was in the upper part of this house he had on the 19th
August, 1727, a zenith sector, of 121/2 feet radius and 121/20 range,
mounted for him by Graham ; even the Observatory at Greenwich
did not possess one till Bradley's was removed there in 1749.
In January, 1730, he propounded his theory of the aberration of
the fixed stars, containing the important discovery of the aberration
of light. He is said to have been led to this, when sailing on the
Thames, by remarking "that every time the boat put about, the
vane at the top of the boat's mast shifted a little, as if there had
been a slight change in the direction of the wind. He observed
this three or four times without speaking ; at last he mentioned it
to the sailors, and expressed surprise that the wind should shift
so regularly every time they put about. The sailors told him the
wind had not shifted, but that the apparent change was owing to the
change in the direction of the boat, and that the same thing invari-
ably happened." (Thomson, "History of the Royal Society.")
From this he inferred that the direction in which we see a star,
is not that in which it actually lies, but is inclined to it by an angle
depending on the direction of the earth's motion round the sun at
the time, and the ratio of its velocity to that of light.
For this discovery he was complimented by the Royal Society,
who discharged him from all future payments.
In the year 1732 his aunt removed with him to Oxford, and he
transferred most of his instruments, leaving, however, the zenith
sector, as he was then engaged in making an extended investigation,
and for the next fifteen years frequently visited Wanstead for the
purpose. The result was his great discovery—a discovery which