Optical toy - Postcards - 1850-1900 - Optical toy

Nine late 19th-century postcards to be viewed by backlighting in day and night vision. Hold-to-light views are constructed in a special way to enable them to be viewed illuminated from the front for a normal 'day' appearance, or illuminated from the back, transforming the view into a 'night' scene, in which hidden colors appear. Some postcards with stamps from 1900. Cards are from Germany with cities like Köln, Mainz, Wiesbaden, Achen, The Netherlands with four of Amsterdam, including Waterloo plein and one from England of Liverpool. Postal stamps from 1900 and 1901.