Mar. 23, 1888.] 



SCIENTIFIC NEWS. 



273 



PASCAL'S VASE. 



THE law of the pressure produced by a column of water 

 is very perfectly illustrated by the apparatus 

 known as Pascal's vase. In the illustration is shown a 

 method of constructing it that is far better adapted to the 

 purposes than the usual one. Several experiments or 

 modifications of experiments can be carried out with it 

 that the regular apparatus does not admit of As shown, 

 it is very simply made, and its construction will be within 

 the capacity of anyone of moderate mechanical ability. 

 For the vase a wide-mouthed bottle is selected. This 

 should have as true a neck as possible, as regards its 

 lower face. The bottom is first cut off This may be 

 executed in various ways, the most reliable, perhaps, 

 being the time-honoured method — with a hot poker. The 

 neck has now to be ground. Some sand is placed upon 

 a glass plate resting on a table, and is well moistened 

 with turpentine. The bottle is held on this, neck down- 

 ward, and rubbed with a circular motion till a flat surface 



filed in them. The beam works upon knife-edges, which 

 are thus constructed. An iron bolt, about three-sixteenths 

 of an inch in diameter, is selected, one which has a long 

 thread being best. Two nuts are required. One is 

 screwed up as far as it will go. A hole is made through 

 the balance beam, and the bolt is thrust through it until 

 the nut comes against the beam. Then the other nut is 

 screwed up so as to hold the beam in place. The pro- 

 jecting portions of the bolt are filed off to a straight and 

 true knife-edge, and the head of the bolt is cut off. If the 

 threaded portion oi the bolt should be too short to admit 

 this treatment, one nut may be reamed out and passed 

 beyond the thread upon the cylindrical portion of the 

 bolt. There it must be secured by soldering. This forms 

 a good abutment for the beam to bear against. Care 

 should be taken to have the bolt perpendicular to the 

 beam. The knife-edges are quite hard enough for the 

 limited work the balance is required for. 



Upon the upper surface, and near the end of the beam, 

 a notch is made. Into the other end, at the upper sur- 



is produced, care being taken to hold it steady, so as not 

 to rock it. The surface thus obtained may be smoothed 

 oiF with ground pumice, used like the sand. The sharp 

 edge, where the bottom was cut off, may be removed by 

 similar grinding, or by a few strokes of a file. If the 

 grinding is well done the bottle, when placed with its 

 open neck downwards, and resting upon a piece of glass, 

 can be filled with water, which it will hold with scarcely 

 any leakage. 



A wooden frame is next made to hold the bottle. A 

 semi-circular opening grasps it tightly near the shoulder, 

 holding it a couple of inches above the base. If it rocks 

 or moves a band of paper can be used as packing to secure 

 it. To close its neck, a plate of perfectly flat glass is cut 

 a little larger than the outside diameter of the neck. The 

 plate may be square, octagon, or circular. The latter is 

 the best shape. 



A support for a balance beam is mortised or screwed 

 fast to the base. A slot is cut in its axis, within which 

 the balance-beam can play. For fulcra, or bearings, for 

 the knife-edges, two wood screws are driven into the top 

 on each side of the slot, and shallow, open grooves are 



tace, an iron pin is driven as near as possible to the 

 centre of the opening of the neck of the bottle when the 

 beam is in its bearings. This pin is filed to a sharp point. 

 A couple of lead weights are arranged to hang from the 

 notched end of the beam. These are easily cast in paper. 

 A sheet of paper is rolled round the end of a round stick 

 of wood, such as a broom-handle, so as to project a couple 

 of inches beyond the wood, and tied securely with string. 

 The paper should be eight or ten layers in thickness. 

 Into the cylindrical cavity thus formed the lead is poured 

 when just melted, and while still fluid the suspending 

 loops are placed in it, and held until all is solid. Two 

 weights ot different sizes should be provided. 



The apparatus is arranged as shown in the cut. The 

 weight holds the glass plate against the bottle, only the 

 sharp point of the pin on the balance touching its under 

 surface. Water is now poured into the vase. If the 

 weight be not too heavy, as soon as a certain level is 

 reached the water will begin to run out between the 

 glass plate and the ground surface of the neck. The 

 level of the water where this occurs is marked by spring- 

 ing arLindia-rubber band round the bottle. This illus- 



