738 Sir J. J. Thomson on the Application of the 



by Vicontini and Omodei (Landolt and Bornstein Tabellen), 

 A = "851, A' = -8298. 



are 



Substituting these values, we find that the difference be- 

 tween the energy of one gramme of potassium in the solid 

 and liquid state is 28 calories, the latent heat of fusion as 

 found by experiment is 16. We have neglected any effect 

 due to the alteration of the specific heats, and A and A' are 

 so close together that a small percentage error in either 

 would produce a large error in their difference. 



We have hitherto confined our attention to cells in the 

 interior of the solid ; let us consider what are the conditions 

 of a cell at the surface. 



A corner of a cell on the surface is the meeting-place of 

 only four cells ; thus only four corners coalesce, and as each 

 corner only carries 1/8 of a charge, the total charge would 

 be 1/2. Now the charge on an electron is the smallest that 

 can exist, so that we cannot represent the state of the surface 

 by placing electrons at the corners of the cells. We must 

 replace this distribution by one where the number of elec- 

 trons is only one-half that of the corners of the cells, i. e., 

 one-half of the number of atoms in the cells at the surface. 

 One symmetrical way of distributing the electrons is, if 

 ABCDEFGrHIJKL represent the atoms below the surface 



i A B C 



E 

 H 

 K 



layer of electrons, to put electrons over BDFHJL but not 

 over ACEGIK. 



We must now consider the forces acting on the surface 

 electrons. Starting from the top of the crystal, we have first 

 a la} r er of electrons with N/2 elections per unit area; next 

 below this we have a layer of positively charged atoms with 

 N atoms per unit area; following this we have a layer of 

 electrons with N electrons per unit area ; and so on. The 

 excess of positive over negative electricity in all the layers 

 below the surface is the amount of electricity in a layer of 

 atoms when there are N/2 atoms per unit area. 



It, as a first approximation, we suppose that the effect of the 

 charges carried by the atoms and electrons in the various 

 layers is the same as if the amount of electricity in the layer 



