Physics 553 



are of the utmost importance in the development of practical 

 aeronautics. In the same year the Smithsonian Report con- 

 tains a paper on " Problems in Flying," by Otto Lilienthal, 

 and another on " Practical Experiments in Soaring," by the 

 same author. The interesting performances of this indefatig- 

 able experimenter are well known, and these short papers, 

 taken in connection with the monographs of Langley, consti- 

 tute a striking illustration of the tremendous advances made 

 in this subject during the past few years. 



In studies of molecular physics nothing has appeared in re- 

 cent years more interesting than the work of Plateau on 

 " Liquid Films and Figures of Equilibrium in Liquid Masses," 

 the first of which appeared in the Smithsonian Report for 

 1863. Few investigations have exhibited more experimental 

 skill than these, and the exquisite illustrations of the laws that 

 determine the equilibrium of liquid films which Plateau de- 

 vised and described render his work classical. The wide 

 publications of these important papers, which were continued 

 from year to year in Smithsonian Reports up to that for 1866, 

 constitute almost an era in the development of our knowledge 

 of surface tension, liquid equilibrium, and capillarity. Among 

 other papers on molecular physics which are to be found 

 in the publications of the Institution, one on " Boscovich's 

 Theory," by Lord Kelvin, in the Report for 1887; another on 

 the " Molecular Structure of Matter," by William Anderson, 

 and still another on " Phenomena Connected with Cloud 

 Condensation," by John Aitken, should have special mention. 

 In the volume for 1893 there is a reprint from the Fort- 

 iiightly Review of Sir Robert Ball's article on " Atoms and 

 Sunbeams," which is a popular presentation of the molecular 

 theory of gases, with an application to the maintenance of the 

 sun's heat. The Report for 1892 reproduces two papers on 

 " Solution," one by Professor Ramsay, and the other by Pro- 

 36 



