Scientific amusements . An optical illusion. Then fix the gaze on the small cross in the picture, andbring the book close up. At a little distance the whiteball will disappear from the page. The illustration shows us a very curious optical ilhision,and one very easy to practise. Roll up a sheet of paper,and look through it» as through a telescope, with the DIVIDED TELESCOPE. 99 right eye, keeping both eyes open. Then place the left handopen palm towards you against the roll of paper, you willthen appear to be looking through a hole in your lefthand-. Sometimes the effect is produced without ho
Scientific amusements . An optical illusion. Then fix the gaze on the small cross in the picture, andbring the book close up. At a little distance the whiteball will disappear from the page. The illustration shows us a very curious optical ilhision,and one very easy to practise. Roll up a sheet of paper,and look through it» as through a telescope, with the DIVIDED TELESCOPE. 99 right eye, keeping both eyes open. Then place the left handopen palm towards you against the roll of paper, you willthen appear to be looking through a hole in your lefthand-. Sometimes the effect is produced without holdingup the other hand to the roll, as shown on page Among optical illusions there are a great number thatmay be produced by means of mirrors. The dividedtelescope is an example. The apparatus, raised on a firmstand, allows of one apparently seeing an object througha stone or other opaque object, as shown in the cut above. lOO OPTICAL ILLUSIONS. The illustration shows the arrangement of the observer, looking through it, plainly perceives theobject through the glass; the image is reflected fourtimes before reaching his eye, by means of small mirrorsconcealed in the instrument.
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Keywords: ., bookcentury1800, bookdecade189, booksubjectscientificrecreations
