PROCEEDINGS OP THE POLYTECHNIC ASSOCIATION. 583 



common hydraulic ram under the same head. The principle applied in this 

 engine is the pressure of water, acting directly upon a reciprocating double- 

 acting piston, working in a horizontal cylinder, which moves two smaller 

 pistons in brass cylinders on either side of the large ones. The small pis- 

 tons alternately force the water through two valves into an air-chamber, 

 and from thence by a small pipe to the point where it is to be used. Di- 

 rectly under the main cylinder is the chest in which are the valves regu- 

 lating the admission and discharge of water, which arc directed in their 

 action by levers at each end moved by the main piston. The machine ex- 

 hibited was about twenty inches long and twenty inches high, including 

 the air-chamber. The diameter of the driving piston is six inches, and that 

 of the forcing piston two i-nches, the ratio of area being as nine to one. The 

 machine is automatic, and when once put in operation under a suflQcient 

 head, near a spring or brook, and properly protected from the frost, will 

 continue to furnish water until the pistons require re-packing. One of 

 these engines was put in motion in the basement of the Cooper Union 

 building, and was there examined by many members after the adjournment. 

 It was regarded as a very compact and complete machine. 



The Chairman then read the following summary of scientific news: 



Periodicity of Earthquakes. 



The influence of the moon upon the fluid covering of the globe having 

 been fully discussed at our last meeting, we may appropriately pass from 

 thei tidal vi&ve to the seismic wave, and briefly allude to the eflect of our 

 satellite upon the fluid nucleus beneath the solid crust of the earth. Prof. 

 A. Perrey, of Dijon, France, affirms " that there is a periodicity as to times 

 of occurrence in earthquakes as in other cosmical and meteorological phe- 

 nomena. When earthquakes, through a long period, are grouped with 

 reference to tlie moon's age, two maxima and two minima of frequency 

 may be distinguished in each lunar month, the maxima following immedi- 

 ately the syzygies, and the minima corresponding to the quadratures. 

 When, again, they are grouped with reference to the passage of the moon 

 over the meridian, there are two analogous maxima and two minima; the 

 maxima corresponding to the passage of the superior and inferior meridian, 

 and the minima to the intermediate times. Tliese laws, based, one on a 

 comparison of more than 6,000 days of earthquakes, and the other on 1,000 

 of earthquake shocks, show that there is a relation between the frequency 

 of earthquakes and the rotation of the moon." The evidence that this rela- 

 tion is one of cause and effect is presented in the leading article of the 

 January number of Silliman's American Journal of Science and Art, 



Porosity of Cast Steel, 



Mr. Deville has given to the Chemical Society of Paris the results of some 

 experiments made by him in connection with Mr. Troost, which prove that 

 cast steel is capable of being penetrated by hydrogen when at a high 

 temperature. He also cited several cases in which heated bodies absorb 

 hydrogen and expel it on cooling. 



