Liquid Vein Demonstration
   The liquid vein demonstration has take on a new life with the advent of lasers and two-litre plastic soda bottles. To do the demonstration, fill the uncolored bottle with water and screw on the cap. Place the bottle at the edge of a table, and shine the laser beam through it. At the exit point, poke a hole with a sharply-pointed awl. When you unscrew the bottle cap, the water comes out in a parabolic arc, with the red laser light following down inside the steam of liquid, thus demonstrating total internal reflection.

   The experiment dates back to the evening of May 19, 1854, when John Tyndall, Professor of Natural Philosophy at the Royal Institution in London, gave a lecture demonstration at the Institution with the title "On some Phenomena connected with the Motion of Liquids." In it he discussed various properties of liquid veins, thin streams of water issuing from holes in the side of a large water tank. At the end of the lecture Tyndall showed how a liquid vein could be used as a pipe to convey light from one place to another. His apparatus was similar to that used shortly afterwards by John Henry Pepper in a demonstration at the Royal Polytechnic Institution at London. The apparatus, including the arc lamp used to generate the light, is shown at the left, below, and at the right, below, is the appearance of the demonstration. 

   The green vertical box at the left is at Hampden-Sydney College in Virginia. It is unmarked, but probably was made ca. 1880 in Europe.

   I found the apparatus at the left in one of the physics demonstration rooms at the University of Texas in Austin during a visit in January 2003. The small orifice half-way up and the glass plate opposite it are standard for the demonstration. The addition of the color wheel is a nice touch. However, the inlet and valve at the bottom are unusual, unless they are part of the mechanism for filling the device with water.

   The apparatus is unmarked, but clearly seems to be made by an apparatus manufacturer. 

REF: Thomas B. Greenslade, Jr.,  "Nineteenth Century Textbook Illustrations LVII...The Liquid Vein", Phys. Teach, 35, 207 (1997)

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