Mr Dunlop's Experiments with Bottles sunk in the Sea. 321 



damp in the small globe which contained the globule of mer- 

 cury, to indicate porosity in the glass. The porter bottle came 

 up full of water as formerly. 



The porter bottle in this, and also in the other experiment, 

 was prepared by Captain Mood, commander of the Portland, 

 who assisted and gave every facility for making experiments, 

 when the weather and circumstances would permit. 



My object with the thermometer, was to ascertain whether an 

 increase of temperature took place at a considerable depth in the 

 ocean ; and not being provided with a self-registering thermo- 

 meter, the only resource I had was to make several about three 

 inches long, and by immersing the bulbs in water heated to a 

 known temperature, the superfluous mercury was forced out, 

 and the moment it began to subside the tube was sealed by the 

 blowpipe. The one which indicated the lowest temperature, 

 required about 73° or 74° of Fahrenheit to raise the mercury to 

 the top of the stem ; but experiment proved the unsatisfactory 

 results I might have expected, as it required a temperature 

 above 80° to burst the slender bulb. The experiments of Cap- 

 tain Sabine and others prove the temperature of the ocean to 

 decrease at considerable depths below the surface. 



I think it can hardly fail to convince any one who makes the 

 experiment of sinking bottles in the sea, and assists personally 

 at the hauling in of the line, that the great force necessary to 

 haul it in must be occasioned by the pressure of the superin- 

 cumbent column of water. And I have no doubt that the same 

 experiment may be performed, and powerful effects produced, 

 on a bottle well corked and secured being placed in a cast-iron 

 cylinder filled with weter, and xhejbrce applied hy a hydrostatic 

 press, on the top of a solid piston (which must be well fitted in- 

 to a smaller cylinder fixed on the top of the larger one), the 

 piston pressing upon the surface of the water in the small cylin- 

 der. And many interesting experiments might be performed in 

 the lecture-room, by substituting a very strong cylinder of glass, 

 having its ends ground parallel, and fitted into brass caps ac- 

 curately ground to fit the outside of the ends of the cylinders, 

 and the bottom of the caps lined with leather, to prevent the 



JULY SEPTEMBER 18^7- X 



