Ixxxiv 



January 15, 1883. 



Dr. J. M. Leete in the chair. Six members present. 



Mr. Nipher gave a lecture on the mathematical theory of poten- 

 tial, illustrating his remarks by plaster models of potential sur- 

 faces. 



February 5, 1883. 



Dr. Engelmann in the chair. Eight members present. 

 Mr. Nipher presented a verbal communication on vortex mo- 

 tion. 



February 19, 1883. 



M. L. Gray in the chair. Seven members present. 



D. S. Brown presented a section of the trunk of a screwr- 

 pine. 



Mr. Nipher presented a model representing the thermodyna- 

 mic surface of steam, showing the i^elation between volume, pres- 

 sure, and temperature. The scale of the model was not large 

 enough to show the departure of the superheated steam from the 

 condition of a perfect gas. The steam line was shown so far as 

 its coordinates are known, and the surface for superheated steam 

 was represented by two sets of threads parallel to the two recti- 

 linear directrices. The condensation surface was also shown 

 by threads representing isothermal lines, which are also lines of 

 equal pressure, stretched between the steam line and the plane of 

 pressure-temperature. 



March 5, li 



M. L. Gray in the chair. Five members present. 

 Mr. N. Holmes made a few remarks on the properties of the 

 aether. 



