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Paul Wing (1996), Stereoscopes. The First One Hundred Years, p.197
According to Wing, George Lowden was the inventor of this type of stereoscope. The patent was put in the name of Ebenezer Scott of Dundee who was acting on his behalf as Patent 2581.
Lowden has been trying to persuade Brewster to adopt some of his improvements to his stereoscope, and in 1906 he wrote in his memoirs of his career in the Dundee Advertiser regarding Brewster:
The fault of Brewster's stereoscope was that the lenses were too small, being, in fact only the two halfs of a spectacle glass. This did not suit every eye, and, in experimenting, I discovered that larger lenses were an advantage. I pointed this out to Sir David, but he was wedded to his own opinion, and, as I feared the idea might be taken up by another, I took out a patent for my improvement, which experience has since been amply justified, but my action was unfortunately resented by Sir David and gave rise to considerable friction for which I did not consider I was to blame, seeing I pointed out the improvement, and he had refused it.