302 PROCEEDINGS OF PROVINCIAL SOCIETIES. 



shewing that when a fluid, as mercury, is poured into one leg of an 

 inverted syphon, it will ascend to the same level in both legs, pro- 

 vided the pressure in both be the same ; and that if water be al- 

 lowed to escape from a vessel filled with it, through an aperture in 

 or near the bottom, the rapidity with which the water flows out 

 will not be uniform, but will diminish in proportion as the height 

 of the column of water in the vessel diminishes : in other words, 

 the quantity that flows out will be unequal in equal times. Such, 

 however, is not the case with sand, as was first shewn, a few years 

 since, by M. Bernard, of Geneva, in describing, to the Philosophical 

 Society of that city, an anemometer, or measurer of the wind, which 

 he had so constructed that the force and direction of the wind were 

 measured by the quantity of sand which escaped from an aperture 

 variable in its size. For this instrument to give accurate results, it 

 was essential that, whatever might be the pressure, equal quantities 

 of sand should flow through the same aperture in equal times ; and, 

 to prove that such is the case, Mons. Bernard instituted a set of 

 experiments on the subject, which led to the knowledge of some 

 very curious and interesting facts. Many of 31. Bernard's experi- 

 ments were repeated during the lecture, by Dr. Corrie. The sand 

 to be used should be well sifted, dry, and not too fine ; that which 

 will pass through a sieve containing thirty-eight wires per inch in 

 one direction, and forty-five or forty-six in the other, flows very 

 readily : but the aperture through which the sand is to flow must 

 not be less than ,079 of an inch in diameter. Part of the apparatus 

 used for exhibiting the experiments was a tin box, open at the top, 

 and provided with an aperture that could be widened or lengthened 

 at pleasure, and the sand that passed out was estimated by measure. 

 It was seen that the quantity of sand that flowed in a given time 

 through a given aperture, was the same, whatever was the weight, 

 the volume, or the height of the sand in the box above. The height 

 of the sand was sometimes increased very considerably, and heavy 

 weights were added to increase the pressure, but without producing 

 any change.* Sand being poured into one leg of an inverted syphon 

 did not ascend in the other, but extended only a very little way into 

 the horizontal part. Whatever pressure may be given to the upper 

 surface of the sand, it exerts no influence on the issue below. An 

 inverted syphon had some mercury poured in until both the limbs 

 were partly filled ; and the sand was then poured in on the one side 

 upon the mercury, but no elevation of the mercury in the other leg 

 took place. If pressure be added to the weight of the sand, still the 

 mercury will remain unmoved. A wafer was pressed against the 



• It was remarked by M. Bernard that there is, perhaps, no other natural 

 force on the earth which produces, by itself, a perfectly uniform movement, 

 and which is not altered, either by gravitation, or friction, or the resistance 

 of the air : for the height of the column of sand has no influence ; friction, in 

 place of being an obstacle, is the regulating cause ; and the resistance of the 

 air within the column must be so feeble as to be altogether insensible as a 

 disturbing force. 



