The following is a paper by H. Aspden published in Physics Essays, v. 4, pp. 13-19 (1991).
Abstract: This paper extends the principles of earlier gravitational theory by which the constant of gravitation G has been deduced in terms of an electrodynamically based graviton theory. Demonstrable anomalous effects reproducible in the laboratory which reveal the prospect of antigravitational action, are discussed. It is shown that the theory does include features which can explain observed antigravitational effects. The action points to vacuum energy fluctuations arising from graviton decay and regeneration. Recently reported weight loss accompanying gyroscopic spin in a non-precessing mode is also explained.
The full text of this paper may also be seen in PDF format as Paper No. 13 in the author's 1996 book Aether Science Papers which is of record in the author's website www.aspden.org.