﻿41.4 Dr. Guyot on the Forms and Forces of Matter. 



and variations will be the subject of special subsequent study ; 

 for the present, and in the first place, I ought to make known 

 how gravitation, attraction, weight, density, cohesion, fusibility, 

 solubility, and affinity are the immediate and necessary conse- 

 quence of the state of vibration of the ponderable molecules of 

 bodies reacting upon the elastic pressure of the imponderable 

 medium which everywhere touches them. 



Here the subject becomes so grave, it is of so much import- 

 ance to science that the theory of universal gravitation should 

 be understood, that I must prepare the minds of my readers by 

 submitting to them material and sensible analogies and palpably 

 verifiable facts. 



If in the atmosphere, an elastic medium possessing at the 

 same time expansibility and definite pressure, we conceive there 

 to be two hemispherical cups of solid matter fitting on to one 

 another exactly by friction, so as to form a sphere like that 

 formed by the Magdebourg hemispheres, we may seek in vain 

 to make them adhere to one another, that is, to give them mu- 

 tual cohesion, if we do not have recourse to the well-known 

 means of rarefying the air within the touching hemispheres. 



As soon as we have, by the air-pump or some other means, 

 diminished the interior pressure on the hemispheres, the two 

 adhere. Their adhesion is small if but little air has been 

 withdrawn ; they have a cohesion almost equal to the total pres- 

 sure of the atmosphere if nearly all the interior air is removed. 



Let us consider the case when the two hemispheres adhere by 

 reason of the withdrawal of, let us say, a hundredth of the air 

 which they contain. They may be separated in three ways : — 

 (1) by applying to each hemisphere an opposite pulling-force 

 equal to 10 grammes per superficial centimetre ; (2) by gently 

 heating the sphere so as to restore to the air in it the hundredth 

 of pressure which it lacks ; and (3) by placing the sphere under 

 the receiver of an air-pump and exhausting the air in this re- 

 ceiver until the external pressure is equal to or less than the 

 internal pressure. In each of these three cases the hemispheres 

 will separate — in the first by rending asunder (arrachement) or 

 overcoming the force of cohesion, in the second by heat-fusion 

 (fusion calorifique) , and in the third by solution {dissolution) in 

 a fluid of equal pressure. 



That which we see take place with two hemispheres we may 

 obtain in the case of a cube formed of eight or twenty seven or 

 other number of little hollow spheres opening into one another 

 at their poles by holes whose edges are ground air-tight. On 

 diminishing the interior pressure, which by its equality with the 

 exterior pressure allows the spheres to move freely among one 

 another, and putting them into exact contact at the moment 



