The English translation is titled "Metaphysics of the Upanishads". Vichar Sagar has been so popular in northern parts of country that it has been used for daily reading for more than centuries by common man who did not have access to Sanskrit scriptures of Vedanta.
Nischal Dasji, who was a Dadu panthi sadhu, had authored many books dealing with Vedanta. Vichara Sagara is the most popular among them. This book is very useful for understanding various prakriyas of Vedanta.
DOWNLOAD Sri Vichar Sagar of Sadhu Nischaldas with Hindi Tika by Pitambara 1917
DOWNLOAD Vichar Sagar English Translation by Lala Sreeram