EXPERIMENTS WITH THE DISPLACEMENT INTERFEROMETER. 71 



ular and not by gravitational force (which is too small). Hence, the method 

 employed should enable the observer to find the density of the concentration 

 in terms of the distance from the plate and the law of attraction of the plate 

 in terms of distance within the small distances in question. In other words, 

 a method for direct investigation of molecular force is here apparently given. 



Correction: The effect of gravity in Chapter II was overestimated and the 

 data have been withdrawn. 



To make an estimate of the gravitational attraction between the largest 

 plates, it is sufficient here to consider the attraction of contiguous disks 

 under the approximate form 



O 



~ . m 2 , m z 



F = 



where ^ = 6.7Xio~ 8 is Newton's constant, a the density, m = ^6& g. the mass, 

 A the area, r= 10 cm. the radius of the disks. We may then write 



. .. m M 



A/v = ?Y 



g<ph(i+mR/Mh) 



and on inserting the value of the variables <p = 01 1 , h = So cm., M = i ,250 g. f 

 ft = 1 1 1 cm. 



equivalent to a little over one-tenth of a vanishing interference ring. Hence 

 the gravitational attraction could not have been recognized, as it was not. 



