IN reply to Prof. Tait's criticism (NATURE, December 31, 1891, p. 199) of my paper (December 17, p. 152), I wish to say that I certainly do not consider Van der Waals's b as an absolute constant.

A group of researchers recently published a paper in the journal ACS Energy Letters that demonstrated the feasibility of using the van der Waals stacking (vdWS) strategy to overcome the inefficiencies ...