"Swift death awaits the first cow that leads a revolt against milking," wrote Swedish Professor Peder Bjornsen just before he died of a heart attack in May 2015.

The spheres, which he called Vitons, are sentient and mildly telepathic (they can read people’s minds if they get close enough); they also feed on the electrochemical energy of human emotions.

Chased into a hospital by a pair of Vitons, Graham and Wohl discover that the phantom vampires shy away from a machine that emits short-wave radio energy.

On pg 63 of the 1966 Paperback Library edition[1] Russell has one of his characters say: The scale of electro-magnetic vibrations extends over sixty octaves, of which the human eye can see but one.

Beyond that sinister barrier of our limitations, outside that poor, ineffective range of vision, bossing every man jack of us from the cradle to the grave, invisibly preying on us as ruthlessly as any parasite, are our malicious, all-powerful lords and masters – the creatures who really own the Earth!Fletcher Pratt, writing in The New York Times, found Sinister Barrier to be a standard adventure story with a scientific background, which moves too fast to let anyone look too closely at parts of the structure.

[4] Dave Langford reviewed Sinister Barrier for White Dwarf #76, and stated that "SF based on Charles Fort's offbeat speculations.

"[5] South Korean writer Djuna cited the work as one that has significantly influenced them in their youth, at the same time noting that "It hasn’t aged well, and it’s particularly criticized for its racist depiction of Asians".