The Earl had a large family to be educated, and there is reason to believe that in his absence from Sion Hariot was intrusted for many years with the confidential supervision of some of the Earl’s personal affairs at Sion, including the education of his children.  How he identified himself with the noble family of his patron may be inferred from these extracts from a letter to Hariot, dated July 19, 1611, of William Lower, one of his loving disciples.  Cecil had been fishing out some new evidence of Percy’s treason from a discharged servant, and was pressing cruelly upon the prisoner.  Lower writes : 

I have here [in South Wales] much otium and therefore I may cast awaye some of it in vaine pursuites, chusing always rather to doe some thinge worth nothing then nothing att all.  How farre I had proceeded in this, I ment now to have given you an account, but that the reporte of the unfortunate Erles relapse into calamitie makes me beleeve that you are enough troubled both with his misfortunes and my ladys troubles; and so a discourse of this nature would be unseasonable. [And concludes the letter with] But at this time this much is to much.  I am sorrie to heare of the new troubles ther, and pray for a good issue of them especiallie for my ladys sake and her five litle ones. [The Countess of Northumberland here referred to was the mother of Sir William Lower’s wife, who was Penelope Perrot, daughter of Sir John Perrot, who married Lady Dorothy Devereux, sister of Essex, and for her second husband Henry Percy the gth Earl of Northumberland.  Lower died in 1615.]

This responsible trust gave Hariot a good house and home of his own at Sion, with independence and an observatory.  He had a library in his own house, and seems to have been the Earl’s librarian and book selector or purchaser for the library of Sion House, as well as for the use of the Earl in the Tower.  The Earl was a great book-collector, as appears by his payrolls.  Books were carried from Sion to the Tower and back again, probably not only for the Earl’s own use, but for Raleigh’s in his History of the World.  Many of these books, it is understood, are still preserved at Petworth, then and subsequently one of the Earl’s seats, but now occupied by the Earl of Leconsfield.

To look back a little.  Before either Raleigh or Henry Percy was shut up in the Tower, we find one of Hariot’s earliest and ablest mathematical disciples, Nathaniel Torporley, a learned clergyman, writing in high praise of him in his now rare mathematical book in Latin, entitled,’ Diclides Coelometricx,’ or Universal Gates of Astronomy, containing all the materials for calculation of the whole art in the moderate space of two tables, on a new general and very easy system.  By Nathaniel Torporley, of Shropshire, in his philosophical retreat, printed in 1602.  The exact title is as follows: 

Diclides Coelometricæ / Seu / Valvæ Astronomicæ / vniversales / Omnia artis totius numera Psephophoretica in sat modicis / finibus duarum Tabularum Methodo noua, generali,/ & facilima continentes./ Authore Nathale Torporlaeo Salopiensi / in secessu Philotheoro. / Londini / Excudebat Felix Kingston. 1602. / 4°.