The Ascent of the Son The Descent of the Spirit. It is now available for free from lulu.com. It comprises 26 Meditations on Ascension and Pentecost.
It is a translation of Op den Pinksterdag (met Hemelvaart), volume 3 of his series Dagen van Goede Boodschap (Kampen: Kok, 1923. It was originally written in 1888 and published posthumously.