CHAPTEE X 

 ON THE DIEECT PEOPEETIES OF MOLECULES 



1O9. Section of the Molecules 



As the investigations in Part I. of this book made it 

 possible to calculate in absolute measure the speed of the 

 molecular movements, so the phenomena discussed in 

 Part II. enable us to determine also in absolute measure 

 the length of the paths traversed by the molecules. All the 

 elements therefore which are concerned in the motion of 

 the molecules are fully known. 



Still, the conclusions which the theory lets us draw 

 respecting the properties of the molecules are not thereby 

 exhausted; and first of all we may seek to determine the 

 extension of the molecules in space. 



When we remember that the length of the paths is 

 determined by the probability of a collision, and that this 

 probability depends on the size of the molecules, it becomes 

 at once clear that the knowledge of their molecular free path 

 enables us to form a judgment as to their extension in 

 space. In 1865, directly after the first experimental in- 

 vestigations of the viscosity of air had led to the knowledge 

 of the free path, Loschmidt 1 made an attempt to deter- 

 mine the sizes of molecules. Later on, in 1867, there 

 appeared two other memoirs with the same aim by my 

 brother Lothar Meyer 2 and Alexander Naumann, 5 



1 Wien. Sitzungsber. 1865, Hi. Abth. 2, p. 395 ; Schl&milch's Zeitschr. f. 

 Math. u. Physik, 1865, 10th year, p. 511. 



2 Ann. Chem. Pharm. 1867, 5. Suppl.-Bd. p. 129. 



3 Ibid. 1867, 5. Suppl.-Bd. p. 252. 



