200 ANNUAL OF SCIENTIFIC DISCOVERY. 



matter, together with the absorption of another portion of water from the mor- 

 tar. To illustrate the process, he supposed a fine capillary tube with its lower 

 end immersed in water, whose internal diameter was sufficiently small to al- 

 low the liquid to rise to the top to be exposed to the atmosphere. Evapora- 

 tion would take place at the upper surface of the column, and new portions 

 of water would be drawn up to supply the loss, and if this process were con- 

 tinued any material which might be contained in the water would be found 

 deposited at the top of the tube, the point of evaporation. If, however, the 

 lower portion of the tube were not furnished with a supply of water, the 

 evaporation at the top would not take place, and the deposition of foreign 

 matter would not be exhibited, even though the tube itself were filled with 

 water impregnated with impurities. The pores of the marble, so long as the 

 blocks remained in the yard, were in this last condition, but when the same 

 blocks were placed in the wall of the building, the water absorbed from the 

 mortar at the interior surface gave the supply of liquid necessary to carry the 

 coloring materials to the exterior surface, and deposit it there at the mouths 

 of the pores. The cause of the phenomenon being known, a remedy was 

 readily suggested; the interior surface of the stone was coated with asphaltum, 

 rendering it impervious to the moisture of the mortar, and the discoloration 

 was gradually disappearing. In a series, of experiments made some ten years 

 ago he had shown that the attraction of the particles for each other of a sub- 

 stance in a liquid form was as great as that of the same substance in a solid 

 form. Consequently, the distinction between liquidity and solidity did not 

 consist in a difference in the attractive power occasioned directly by the re- 

 pulsion of heat ; but it depended upon the perfect mobility of the atoms, or a 

 lateral cohesion. He might explain this by assuming an incipient crystalliza- 

 tion of atoms into molecules, and consider the first effect of heat as that of 

 breaking down these crystals and permitting each atom to move freely around 

 every other. ."When this crystalline arrangement was perfect, and no lateral 

 motion was allowed hi the atoms, the body might be denominated perfectly 

 rigid. "We had approximately an example of this in cast steel, in which no 

 slipping took place of the parts on each other, or no material elongation of the 

 mass ; and when a rupture was produced by a tensile force, a rod of this ma- 

 terial Was broken with a transverse fracture of the same size as that of the 

 original section of the bar. In this case every atom was separated at once 

 from the other, and the breaking weight might be considered as a measure of 

 the attraction of cohesion of the atoms of the metal. The effect, however, was 

 quite different when we attempted to pull apart a rod of lead. The atoms or 

 molecules slipped upon each other. The rod was increased in length and dimin- 

 ished in thickness until a separation was produced. Instead of lead we might 

 use still softer materials, such as wax and putty, until we arrived at a substance 

 in a liquid form. This would stand at the extremity of the scale, and between 

 extreme rigidity- on the one hand and extreme liquidity on the other, we might 

 find a series of substances gradually shading from one extremity to another. 

 According to the views he had presented, the difference in tenacity of steel 

 and lead did not consist in the attractive cohesion of the atoms, but in their 

 capability of slipping upon each other. From this view it followed that the 



