At Cambridge, Hartley studied with Nicholas Saunderson, who, though blind since infancy, became the fourth Lucasian Professor of Mathematics. Hartley was later instrumental in raising the subscription for the posthumous publication of Saunderson's "Elements of Algebra" (1740). Upon graduation, Hartley declined to sign the Thirty-nine Articles, a requirement for ordination in the Church of England. Although one point at issue may have been the doctrine of the Trinity, Hartley's main dissent from orthodox teaching was his commitment to universal reconciliation. Writing to his friend Joseph Lister in 1736, Hartley stated he believed "That Universal Happiness is the Fundamental Doctrine both of Reason & Scripture", adding that "nothing is so irreconcilable Reason as eternal Punishment, nothing so contrary to all the Intimations God has given us in his Works. Have you read Sr. Is. Newton’s Commt. upon Danl. & the Apocalypse?" For Hartley, on the gates of hell there could be no locks.