593 



drawn inward is J0700 atinospiieres or 1085 XlQi" dynes per cm." 

 (van der Waals). 



The more central molecules attract each other no less; thej' also 

 attract each other with a force of 1Ü85X1^0'0 dynes, because the 

 sphere of action of this attraction does not extend beyond the diameter 

 of one molecule. The i-adius of this sphere (rj is stated as 1-5 > 10—^ cm. 

 (Minkowski), the diameter of a molecide being 29 x, K)— *. 



There are about 3-45 x 10' molecules to a cm., hence there is 

 the same number of layers. In the three directions of the sides 

 of 1 cm' of water, we find 3 x 1-085 x 10" K 345 X 10' — 112 X 

 1018 dynes of total intermolecular force. That the sphere of action 

 is smaller than the dianieler of one molecule, on which the correctness 

 of the amount 112 ■ lO^» is based, may be verified by considering 

 the amount of heat necessary to evaporate 1 gram of water or even 

 of ice (0-62 calorie) as a measure of the work required to split up 

 J gram into loose molecules. This work amounts to 260 K.gr.m., 

 for 1 gram of ice, or 26 > lO^o erg. From tlie equation 2-6 X lO^" erg 

 = 3 X 1-085 X 1010 dynes X 3-45 X 10" > r,we find r ^ 2-31 X lO'», 

 hence smaller than the diametei' of one molecule. 



How much attraction do we find in platinum or in paraffin? 



Van der Waals states that the intermolecular pressure is proportional 

 to the sp. gr'. This is also true of the sum of the attractions. In 

 balls of the same size it is therefore also proportional to thesp.gr', 

 but in balls of the same weight, to the sp. gr.', provided there 

 are equal numbers of layers of molecules per cm.', which however 

 is not the case. The sp. gr. of platinum being 21-5 and the molecular 

 weight 194, it can l>e calculated that there are 1-26 X the number 

 of molecules in water per em". In like manner it can be calculated 

 for paraffin, sp. gr. 0-87 and molecular weight (C^jH^) 286, that it 

 contains per cm.' 0.38 X the number of molecules in water per cm.'. 



In 1 gram of water we found the total intermolecular attraction 

 to be 1.12 X 101^ dynes, we derive from this for 

 1 gram of platinum M2 X lOi» >, 21-5 X 1-26 = 30-5 ;>' lOis dynes 

 1 gram of paraffin J 12 lO'» X 087 X 0-38:= 037 X lO's dynes 

 in platinum per gram an excess of 30 X lOi^dynes. 



If the motion of the ether through the two balls had caused any 

 aberration, we might reasonably assume that of the 0-37x101^ dynes 

 per gram of paraffin an equal fraction had been diverted as of 

 037X101^ dynes in platinum; aberration-angles and aberration- 

 components, which may accompany them, are exclusively based on 

 ratios of velocity, and not on ratios of distance. The equal amounts 



