616 Dr. A. C. Crehore on the Construction of 



where the <r-force is zero. The systems o£ ^-force curves are 

 all tangent at the origin to either the ^-axis or to the curve 

 for F z = 0. The force changes sign in crossing the curve o£ 

 zero force, being negative above and positive below this 

 curve. A positive z-t'orce means that the second atom urges 

 the atom at the origin upward in the positive direction. If 

 the second hydrogen atom is on the s-axis above the origin 

 where the ^-force is negative the atoms repel each other. 

 The zero curve for z beyond the limits of the chart forms a 

 loop coming around and intersecting the r-axis at a distance 

 of 1682 units. Here the force changes sign from a repulsion 

 to an attraction, and there is a position of stable equilibrium 

 for the two atoms. The .r-force is zero along this z axis. 

 Along the #-axis, on the other hand, the r-force is zero and 

 the #-force always positive, indicating an attraction between 

 two hydrogen atoms at any distance when one is on the 

 equator of the other. The force in this direction is not zero 

 at any distance. The rate of diminution of the force near 

 the origin in all directions is as the inverse fourth power of 

 the distance. At a great distance from the origin the law 

 changes, so that the force is inversely as the square of the 

 distance. 



The character of the field between carbon and hydrogen, 

 shown in fig. 2, is strikingly different from that of fig. 1. 

 The most noticeable difference is that there are two angles 

 where the 2-force is zero in the first quadrant, and the only 

 region where the 2-force is positive is between these two zero 

 curves. It is negative in the region near the ^-axis and the 

 .^-axis. The 2-force on the #-axis is zero and is a maximum 

 on the 2-axis. On the other hand, the #-force is zero on the 

 2-axis and a maximum on the ^-axis. In great contrast to 

 fig. 1 the <2?-force is negative on the equator, showing a 

 strong repulsion between hydrogen and carbon or between 

 carbon and carbon in this situation, whereas the hydrogen 

 attracts hydrogen. This fact has a very significant bearing 

 upon the compound-forming processes. 



Another striking difference is in the rate of diminution of 

 the forces with the distance. At small distances, which 

 includes all distances on this chart, the force decreases as the 

 inverse sixth power of the distance, and at great distances 

 as the inverse fourth power of the distance. 



These figures show only the forces in one quadrant, but a 

 section of the field on a much reduced scale for the four 

 quadrants is shown in PI. X. fig. 3 for the case of hydrogen 

 acting on hydrogen, and in PL XL fig. 4 for the case of 

 carbon on hydrogen. The complete fields in space may 



