THE PROGRESS OF SCIENCE 



615 



THE PEOGEESS OF SCIENCE 



RUTHERFORD ON TEE CONSTI- 

 TUTION OF MATTER 



The most notable features of the 

 annual meeting of the National Acad- 

 emy of Sciences held, in Washington in 

 the third week of April were two lec- 

 tures by Sir Ernest Kutherford, the 

 distinguished physicist of the Univer- 

 sity of Manchester. These are the first 

 of a series of lectures, established by 

 the children of William Ellery Hale, 

 which are to treat problems of evolu- 

 tion from the atom to man. At the au- 

 tumn meeting of the academy, stellar 

 evolution will be reviewed by Dr. W. 

 W. Campbell, director of the Lick Ob- 

 servatory. Sir Ernest's lectures, which 

 were reported stenographically, will be 

 printed in Science and ultimately in a 

 book with the other lectures of the se- 

 ries. It is almost impossible to repre- 

 sent their contents by an abstract, but 

 in view of the great interest and im- 

 portance of the subject and the orig- 

 inality of some of the experiments and 

 theories, it may be well to attempt to 

 give an outline. 



Sir Ernest began by reminding his 

 audience that the idea that matter is 

 composed of very minute discrete par- 

 ticles incapable of subdivision and 

 therefore called atoms was familiar to 

 the Greeks, atom in their language 

 being equivalent to the indivisible. 

 This idea was little developed until the 

 beginning of the last century when Dal- 

 ton first applied it to the chemical con- 

 stitution of compounds showing that 

 each separate element such as oxygen, 

 iron, nitrogen, etc., always combines in 

 a certain definite equivalent proportion. 

 This is in fact the basal conception of 

 modern chemistry and renders it pos- 

 sible to derive the composition of 

 a substance from a chemical analysis. 

 Chemistry thus lent exceedingly strong 

 support to the hypothesis of the 



atomic constitution of matter, but 

 no further advance in the subject 

 was made till about the middle of 

 the century when the so-called kinetic 

 theory of gases was developed by 

 Clausius and Maxwell. This theory ac- 

 counts for the pressure and other 

 properties of gases by supposing them 

 constituted of single atoms, or of small 

 groups of atoms united into molecules, 

 moving with an amount of energy 

 which is proportional to the tempera- 

 ture. The mathematical developments 

 of this theory and the conclusions to be 

 drawn from the f ormulas have been veri- 

 fied in cases so very numerous that no 

 one now or for a long time has doubted 

 the essential correctness of the under- 

 lying hypothesis. In spite of the con- 

 viction that the kinetic theory was true, 

 it was for long supposed that no ac- 

 tual demonstration of atomic or molec- 

 ular structure could ever be reached. 

 Of late years, however, the study of an 

 almost forgotten phenomenon called the 

 Brownian movement has led to actual 

 demonstrations. Brown as long ago as 

 1827 observed that microscopic spores 

 of plants suspended in a liquid were in 

 constant motion. The smaller the par- 

 ticles the more actively they were dis- 

 placed while their movements were 

 thoroughly irregular, the spores passing 

 one another in opposite directions or 

 intersecting one another's paths with- 

 out any general drift such as would 

 have resulted from ordinary currents in 

 the fluids due, for example, to differ- 

 ences of temperature. Of late years 

 this Brownian movement has been stud- 

 ied with great precision by M. Perrin 

 and others. It has been established that 

 particles sufficiently small, say one ten- 

 thousandth of an inch in diameter, are 

 really displaced in a random manner by 

 the vastly smaller invisible molecules of 

 the fluid in which they are suspended, 

 and that the movements of the mole- 



