elder brother, Francis, died in 1600 at the age of 78, so that he was
born in 1522. It is not unreasonable to suppose that William, his
brother, one of a large family, was born between the years 1525 and
1527. He would therefore be somewhere between 44 and 46 years of age,
when he discovered the medicinal qualities of the Tuewhit Well, which
equally accords with Deane's statement that in his younger days he had
travelled in Germany.

So far as I can trace, Hargrove[12] is the first author to confuse the
uncle and the nephew. He writes that the well

"was discovered by Capt. William Slingsby, about the year 1571.
This Gentleman, in the early part of his life, had travelled in
Germany, where he made himself acquainted with the Spaws of that
country. He lived sometime at Grange House, near the Old Spaw, from
whence he removed to Bilton Park, where he spent the remainder of
his days. He made severall trials of this water, and finding it
like the German, he walled it about, and paved it at the bottom,
leaving a small opening for the free access of the water. Its
current is always near the same, and is about the quantity of the
Sauvenir, to which Mr. Slingsby thought it preferable."

From this quotation it is clearly apparent that Hargrove erroneously
inferred that Mr. Slingsby and Capt. Slingsby were the one and the same
person instead of being uncle and nephew. In the 3rd edition of the
"History of Knaresborough," published in 1782, the reference to Mr.
Slingsby is omitted and from that edition onwards, Captain Slingsby
appears as the discoverer of the Tuewhit Well in 1571, a discovery
clearly inconsistent with the fact that he was born in the year 1562.