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The stereoscope was a major source of entertainment for folks before television was invented.
Your cards were published circa 1906 - 1908.
If the viewer and the cards are all in excellent condition, the current value of the cards is approximately $150 for the set and the value of the viewer is approximately $125. Those are the retail(insurance or replacement) values. If you were to sell these, you could expect to get the fair market (private sale or auction) value of approximately 40% of the retail amount, or $60 for the cards and $50 for the viewer, depending on location and actual condition.
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