FLU 



FLU 



I 



tibles. They combine with silica by means 

 of heat. 



FLUENT, in fluxions, the flowing 1 ' 

 quantity, or that which is continually 

 either increasing or decreasing, whether 

 line, surface, solid, &c. See FLUXION. 



FLUID, in physiology, an appellation 

 given to all bodies, whose particles easily 

 yield to the least partial pressure or force 

 impressed. 



All fluids, except those in the form of 

 air or gas, are incompressible in any con- 

 siderable degree. The Academy del Ci- 

 mento, from the following experiment, 

 supposed water to be totally incompressi- 

 ble. A globe made of gold, which is less 

 porous than any other metal, was com- 

 pletely filled with water, and then closed 

 up ; it was afterwards placed under a great 

 compressive force, which pressed the 

 fluid through the pores of the metal, and 

 formed a dew all over its surface, before 

 any indent could be made in the vessel. 

 Now, as the surface of a sphere will con- 

 tain a greater quantity than the same sur- 

 face under any other form whatever, the 

 academy supposed that the compressive 

 power which was applied to the globe 

 must either force the particles of the fluid 

 into closer adhesion, ordrive them through 

 the sides of the vessel before any impres- 

 sion could be made on its surface ; for al- 

 though the latter effect took place, it fur- 

 nishes no proof of the incompressibility of 

 water, as the Florentines had no method 

 of determining that the alteration of 

 figure in their globe of gold occasioned 

 such a diminution of its internal capacity, 

 as was exactly equal to the quantity of 

 water forced into its pores ; but this expe- 

 riment serves to shew the great minute- 

 ness of the particles of a fluid in penetrat- 

 ing the pores of gold, which is the densest 

 of all metals. Mr. Canton brought the 

 question of incompressibility to a more 

 decisive determination. He procured a 

 glass tube, of about two feet long, with a 

 ball at one end, of an inch and a quarter 

 in diameter : having filled the ball and 

 part of the lube with mercury, and brought 

 it to the heat of 50 of Fahrenheit's ther- 

 mometer, he marked the place where the 

 mercury stood, and then raised the mer- 

 cury by heat to the top of the tube, and 

 there sealed the tube hermetrically ; then, 

 upon reducing the mercury to the same 

 degree of heat as before, it stood in the 

 t ube _32_ of an inch higher than the mark. 

 The same experiment was repeated with 

 water, exhausted of air, instead of mercu- 

 ry, and the water stood in the tube ^ 



above the mark. Now, since the weight 

 of the atmosphere on the outside of the 

 ball, without any counterbalance frovrr 

 within, will compress the ball, and equally 

 raise both the mercury and water; it ap- 

 pears that the water expands J- 1 - of an 

 inch more than the mercury, by removing 

 the weight of the atmosphere. From 

 this, and other experiments, he infers* 

 that water is not only compressible, but 

 elastic ; and that it is more capable of 

 compressibility in winter than in summer. 

 All fluids gravitate, or weigh, in pro- 

 portion to their quantity of matter, not 

 only in the open air, or in vacuo, but in 

 their own elements. Although this law 

 seems so consonant to reason, it has been 

 supposed by ancient naturalists, who were 

 ignorant of the equal and general pres- 

 sure of all fluids, that the component parts, 

 or the particles of the same element, did 

 not gravitate or rest on each other; so 

 that the weight of a vessel of water balanc- 

 ed in air would be entirely lost, when the 

 fluid was weighed in its own element. 

 The following experiment seems to leave 

 this question perfectly decided : take a 

 common bottle, corked close, with some 

 shot in the inside to make it sink, and 

 fasten it to the end of a scale beam ; then 

 immerse the bottle in water, and balance 

 the weight in the opposite scale ; after- 

 wards open the neck of the bottle, and let 

 it fill with water, which will cause it to 

 sink ; then weigh the bottle again. Now 

 it will be found that the weight of the 

 water which is contained in the bottle is 

 equal to the difference of the weights in 

 the scale, when it is balanced in air ; which 

 sufficiently shews that the weight of the 

 water is the same in both situations. As 

 the particles of fluids possess weight as 

 a common property of bodies, it seems 

 reasonable, that they should possess the 

 consequent power of gravitation which 

 belongs to bodies in general. Therefore, 

 supposing 1 that the particles which com- 

 pose fluids be equal, their gravitation 

 must likewise be equal ; so that in the 

 descent of fluids, when the particles are 

 stopped and supported, the gravitation 

 being equal, one particle will not have 

 more propensity than another to change 

 its situation, and after the impelling force 

 has subsided, the particles will remain at 

 absolute rest. 



From the gravity of fluids arises their 

 pressure, which is always proportioned 

 to the gravity. For if the particles of 

 fluids have equal magnitude and weight, 

 the gravity or pressure must be proper- 



