that the way to cognizing the spiritual world is based on the natural scientific attitude, and that certainty of such knowledge is comparable to the certainty found in mathematics and natural science.
Drawn from Schiller’s notebooks, this important volume describes natural scientific research by scientists working at the Goetheanum and following suggestions from Rudolf Steiner, leading, for example, to research on gases at low temperatures and high vacuum. The Schiller File is an important resource for those who wish to better understand how to approach and practice natural science from the perspective of spiritual science
http://www.rudolfsteinerpress.com/pages/viewbook.php?isbn_in=9780880107204