And he taught them that after Jesus had manifested himself to his disciples to be that Christ that was crucified, dead and buried; and by his appearing and conversing with his disciples for the space of forty days after his resurrection, he then, and not till then, ascended into heaven in the sight of those disciples; namely, on that day which we call the ascension, or Holy Thursday. And that we then celebrate the performance of the promise which he made to his disciples at or before his ascension; namely, “that though he left them yet he would send them the Holy Ghost to be their comforter;” and that he did so on that day which the Church calls Whitsunday.* Thus the Church keeps an historical and circular commemoration of times, as they pass by us; of such times as ought to incline us to occasional praises, for the particular blessings which we do, or might receive, by those holy commemorations.
From ‘The Life of Mr George Herbert (1670) by Izaak Walton (1593-1683).
* Its more technical name is Pentecost, indicating the fiftieth day after Passover; it was originally a Jewish feast of the Spring harvest. The English name Whitsunday, or White Sunday, derives from the very early tradition that christenings were held on this day, as they were on all the Sundays from Easter to Pentecost, for which white robes were used.