Liquid Level Vases
   The Liquid Level Vase is sometimes called Pascal's Vase, although I have chosen to use this name for a device used for quantitative measurements. 

   Demonstrations with the Knott vase at the Smithsonian (left) and the Queen Vase at Virginia Military Institute (right) start with the large glass vase full of water. The stopcock is opened and the water flows into the crooked tube. When equilibrium is reached, the water levels in both the tube and the vase are the same. 

   The unmarked liquid level vase at the right is on display at the University of Cincinnati physics department.

   Liquid Level Vases with multiple tubes are shown in the four examples below. The Cincinnati apparatus is by Queen and cost $12.00 in the 1881 catalogue. The St. Mary's apparatus is the economy model from the same catalogue and cost $3.50. The apparatus in the Smithsonian collection was made by the L. E. Knott Apparatus Co. of Boston, and cost $3.30 in the 1916 catalogue. The demonstration is a hardy evergreen, and is still in modern apparatus catalogues.
                              Yale University                                                             University of Cincinnati
                     Smithsonian Institution                                                           St. Mary's College
   This is another example of a Queen equilibrium vase, as it is referred to in the 1888 catalogue. There were originally six vases, including a short one with a narrow orifice at the top that shot up a tiny fountain. The top of the spray almost reached the level of the large supply vase.

   This apparatus is in one of the lecture demonstration rooms in the physics department at the University of Texas in Austin. The original color of the base was black, probably with concentric gold pinstripes. 

   At the left is a liquid level vase from the Millington/Barnard Collection at the University Museum at the University of Mississippi in Oxford. 

   It is unmarked, but in the second half of the 1950's Prof. Frederick Barnard bought a good deal of apparatus from the firm of Lerebours et Secretan of Paris. 

   The version of the liquid-level vase at the right is sometimes called Haldat's Apparatus. The apparatus at the right very closely follows an illustration in the 1875 edition of Ganot's Physics. The accompanying quote is: "It consists of a bent tube [on the bottom] at one end of which is fitted a stopcock, in which can be screwed two vessels, of the same height, but different in shape and capacity, the first being conical and the second nearly cylindrical. Mercury is poured into the [horizontal] tube until its level nearly reaches [the top of the upward bend of the tube]. The [conical] vessel is then screwed on and filled with water. The pressure of the water acting on the mercury causes it to rise in the cylindrical tube, and its height may be marked with a small collar which slides up and down the tube. The height of the water in [the conical vessel] is also marked. When this is done, [the conical vessel] is emptied by means of the stopcock [seen projecting toward the viewer], unscrewed and replaced by [a vessel of a different shape]. When water is now poured into this, the mercury, which had resumed its original level in [the horizontal tube] rises in the cylindrical tube, and when the water in the [new vessel] has the same height as it had [before], ... the mercury will have risen to the height it had before. ... Hence the pressure on the mercury in both cases is the same. This pressure is therefore independent of the shape of the vessels, and, consequently, also of the quantity of liquid." 
   This apparatus is in the Garland Collection of Classic Physics Apparatus at Vanderbilt University in Nashville, Tennessee.

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