176 SEE— FURTHER RESEARCHES ON [April 24, 



considerations was obtained by J\I. Lippmann, in a paper read to the 

 Paris Academy of Sciences, October 16, 1882. 



In his " Popular Lectures and Addresses " (vol. i, p. 224) Lord 

 Kelvin condenses his conclusions as follows : 



" The four lines of argument which I have now indicated lead all to 

 substantially the same estimate of the dimensions of molecular structure. 

 Jointly they established, with what we cannot but regard as a very high 

 degree of probability, the conclusion that, in any ordinary liquid, transparent 

 solid, or seemingly opaque solid, the mean distance between the centres of 

 contiguous molecules is less than the 1/5,000.000 and greater than the 

 1/1,000,000,000 of a centimeter. 



" To form some conception of the degree of coarse-grainedness indi- 

 cated by this conclusion, imagine a globe of water or glass, as large as a 

 football,' to be magnified up to the size of the earth, each constituent mole- 

 cule being magnified in the same proportion. The magnified structure would 

 be more coarse grained than a heap of small shot, but probably less coarse- 

 grained than a heap of footballs." 



§ II. On the Molecular Constitution of Matter and on the Pene- 

 trability of Solids by Fluids. — In his address on " Mathematical 

 Physics " at the St. Louis Congress of Arts and Sciences in 1904, 

 Poincare speaks of the porosity of matter as follows : 



" The astronomical universe consists of masses, undoubtedly of great 

 magnitude, but separated by such immense distances that they appear to us 

 as material points ; these points attract each other in the inverse ratio of the 

 squares of their distances, and this attraction is the only force which affects 

 their motion. But if our senses were keen enough to show us all the details 

 of the bodies which the physicist studies, the spectacle thus disclosed would 

 hardly differ from the one which the astronomer contemplates. There too 

 we should see material points separated by intervals which are enormous 

 in comparison with their dimensions, and describing orbits according to 

 regular laws. Like the stars proper, they attract each other or repel, and 

 this attraction or repulsion, which is along the line joining them, depends 

 only on distance." (Cf. Bulletin of the American Matliematical Society, 

 February, igo6, p. 241 ; authorized translation by Professor J. W. Young.) 



Professor Sir G. H. Darwin's recent presidential address to the 



British Association for the Advancement of Science at Cape Town, 



1905, was devoted largely to the discovery of electrons. After 



treating of these subatomic corpuscles he adds : 



" I have not as yet made any attempt to represent the excessive minute- 

 ness of the corpuscles, of whose existence we are now so confident; but, as 

 an introduction to what I have to speak of next, it is necessary to do so. 



' Or say a globe of 16 centimeters diameter. 



