ON THE NON- PERMEABILITY OP GLASS BY WATER. 75 



As the experiments made by Mr. Rudder and Mr. Benson were 

 considered inconclusive, in relation to the question of the porosity 

 of glass, or its permeability by water, (the pressure of a column of 

 water of 900 feet, the depth to which their bottles were plunged, 

 not exceeding a pressure of 450 pounds on the square inch), Mr. 

 Wickenden, with the assistance of an intelligent member of the In- 

 stitution, proceeded to make the following experiments. Glass balls, 

 varying in size and thickness, were hermctrically sealed, and sub- 

 jected to a pressure of 1050 pounds on the inch ; that is equivalent 

 to the weight of a column of water of about 2000 feet, or 350 fa- 

 thoms, exceeding the pressure to which the bottles were exposed by * 

 200 fathoms. The integrity of the globes was maintained in this 

 experiment, and not a drop of water entered. In order to submit 

 the globes to the greatest accessible pressure, it was determined to 

 place them in the plunger of Bramah's hydraulic press. The balls, 

 which were three inches in diameter, were inclosed in a box, perfo- 

 rated to admit the water, and after being subjected to a superficial 

 pressure of between eighteen and nineteen tons, or about a ton and 

 a half on the square inch, (which is equal to a column of water of 

 1120 fathoms, or 6720 feet, that is, a weight of 3360 pounds on the 

 square inch) they were taken out uninjured, and perfectly free 

 from internal moisture. 



From the whole of the foregoing experiments, the following con- 

 clusions may be drawn. 1st. It appears extremely difficult, by stop- 

 ping the mouths of bottles with extraneous m^atters, such as cork, 

 wood, pitch, &c., to resist the stupendous weight of columns of 

 water of great altitude. 



2ndly. That at a depth of 150 fathoms, or 900 feet, — that is, 

 with a pressure of about 4501bs. on the square inch, glass is not 

 permeable by water. 



By the experiments made with glass balls, the difficulties of stop- 

 ing are overcome, whilst a form is employed better adapted to resist 

 the higher degrees of pressure ; and the presumptive evidence of the 

 non-porosity of glass, or rather impermeability by water, is greatly 

 increased. 



The question assumed as proved by Mr. Rudder's experiments, is 

 the non-porosity of glass. The transmission of light and magnetic 



