As in the first Prayer Book, the origins and participants in the work of its revision are obscure, but it was clear that Cranmer led the project and steered its development. It had begun as early as the end of 1549 when the Convocation of Canterbury met to discuss the matter. Late in 1550, the opinions of Martyr and Bucer were sought on how the liturgy might be improved and they significantly influenced the revision. The spiritual presence view was clarified by the use of entirely different words when the communicants are offered the bread and the wine. New rubrics noted that any kind of bread could be used and any bread or wine that remained could be used by the curate, thus disassociating the elements from any physical presence. The new book removed any possibility of prayers for the dead, as such prayers implied support for the doctrine of purgatory. The Act of Uniformity 1552, which authorised the book's use, specified that it be exclusively used from 1 November. The final version was officially published at nearly the last minute, due to Dudley's intervention. While travelling in the north of the country, he met the Scots reformer, John Knox, then based in Newcastle. Impressed by his preaching, Dudley selected him to be a royal chaplain and brought him south to participate in the reform projects. In a sermon before the king, Knox attacked the practice of kneeling during communion. On 27 September 1552, the Privy Council stopped the printing of the new Prayer Book and told Cranmer to revise it. He responded with a long letter using the argument that it was for Parliament with the royal assent to decide any changes in the liturgy. On 22 October, the council decided to keep the liturgy as it is and add the so-called "Black Rubric", which explained that no adoration was intended when kneeling at communion.