Definition of "stereopticon"

The stories did not seem to me to touch life. […] They left me with the impression of a well-delivered stereopticon lecture, with characters about as life-like as the shadows on the screen, and whisking on and off, at the mercy of the operator.

1897 December (indicated as 1898), Winston Churchill, chapter I, in The Celebrity: An Episode, New York, N.Y.: The Macmillan Company; London: Macmillan & Co., Ltd.

Certain unscrupulous individuals grow rich through the manufacture and distribution of suggestive postcards, obscene steriopticon views, and inexcusable books and typewritten pamphlets.

1930, Jefferis & Nichols, Safe Counsel or Practical Eugenics, page 200