Record. xxxv 



sary of the founding of the Philadelphia Academy of 

 Natural Science as the representative of the Academy. 



Professor J. L. Van Ornum spoke on "The Permea- 

 bility of Concrete and Methods of Securing Impermea- 

 bility." 



Professor Van Ornum reviewed the methods practicably applicable 

 to prevent dampness in rubble masonry foundation walls; that is, by 

 drainage or by an impervious coating of their exterior, or by both. He 

 then referred to the general use at present of concrete foundation 

 walls for important structures and the necessities for securing their 

 impermeability. This may be attained by constructing an impervious 

 diaphragm of a bituminous material; by an efficient surface coating, 

 preferably on the outside; by carefully securing a maximum density 

 by propeiiy proportioning the components of the concrete; or by mix- 

 ing with the concrete certain colloidal (or other) substances to secure 

 this result. The latter two methods have been experimentally investi- 

 gated in successive years as thesis work by H. P. McFarland, P. C. 

 Grace, S. Johnson, and W. K. Begeman. Their results agree in gen- 

 eral with those of others in concluding that, for any usual conditions, 

 the patented mixtures sold for this purpose vary in effectiveness 

 from very poor to very good; and that proper proportioning of the 

 constituents of the concrete to attain a maximum density, such as is 

 desirable to secure a maximum strength, will also effect practical 

 impermeability; but they differ from the conclusions of some others 

 in the fact that they found no advantage to result from the incorpo- 

 ration of such a material as hydrated lime in the richer mixtures. 



The apparatus designed by the students for these experiments, 

 which gave pressure up to foi'ty pounds per square inch, was planned 

 to eliminate certain features of the experimental devices of other 

 tests which seemed objectionable to them; particularly in eliminating 

 tensile stresses from the specimens tested, with the resulting ten- 

 dency to form cracks. It is such development of the student's initi- 

 ative and his responsibility in adapting his methods to conditions so 

 as to secure the desired results which constitute the most valuable 

 experience in the work of graduation theses. 



Dr. Geo. 0. James then addressed the Academy on 

 "The Application of the Relativity Law of Gravitation 

 to the Motion of the Perihelion of Mercury." 



Professor F. E. Nipher gave a preliminary account of 

 work he has been doing on the effect of a disruptive dis- 

 charge through a fine wire. 



Plante discovered that the wire buckles. He ascribed the phenom- 

 enon to rapid vibrations of more or less elastic matter, brought about 

 by the propagation of the "electric movement." 



Professor Nipher is experimenting on a very delicately suspended 

 wire, with a view of determining whether the longitudinal thrusts 



