412 



Messrs. Carpenter, Jeffreys, and Thomson [Nov. 18, 



me.'elv on shore, but also on board the 'Porcupine' when lying in dock or 

 harbour. But it could not be worked with the Galvanometer supplied 

 when there was the least roll of the vessel ; for it was then found impossible 

 to make the zero observations requisite to indicate equilibrium, though 

 Mr. W. L. Carpenter (who had charge of the apparatus, p. 403) tried 

 every expedient that circumstances admitted. It is obvious, therefore, 

 that this instrument can only be made use of on board ship when the 

 Galvanometer is so suspended as not to participate in the rolling or pitching 

 of the vessel ; and it is to be hoped that Mr. Siemens, with his well- 

 known ingenuity, may be able to devise the means of accomplishing this. 



18. It may be well here to mention that as it was found impracticable to 

 employ Mr. Siemens' s Differential Thermometer for the determination of 

 the question whether the minimum temperature registered by the Thermo- 

 meters is the actual bottom temperature, or is the temperature of some 

 intermediate stratum, this was effected by taking series of Temperature 

 Soundings with Thermometers sent down to successively increasing depths 

 in the same locality. Such series were obtained in each of the Cruises ; with 

 the result, as will be shown hereafter ( §94 etseq.), of not merely confirming the 

 conclusion advanced in the 1 Lightning' Report (p. 189) that the minimum 

 temperature is that of the bottom, but of affording a set of most important 

 data for a general doctrine of the interchange between Equatorial and 

 Polar waters in the great Oceanic basins. 



19. The next subject considered by the Scientific Committee was the feasi- 

 bility of constructing a vessel which should fill itself with Water, either at 

 the bottom or at any intermediate depth, as might be required ; and which 

 should bring such water to the surface without the loss of any of the 

 Gases dissolved in it. This might be easily accomplished, were it not 

 for (1) the expansion which water taken under great pressure undergoes 

 when that pressure is removed, the force of which would be sufficient 

 to burst the strongest vessel that could be made ; and (2) the expansile 

 force of the gases dissolved in it under great pressure, which would exert 

 itself in the same direction. Various plans were suggested for meeting 

 this difficulty ; but it was considered that as time would not permit of the 

 preparation of any but very easily constructed apparatus, it would be 

 better on the present occasion to adopt a form of Water-Bottle suggested 

 by the Hydrographer on the basis of the cylindrical copper cases used for 

 the protection of deep sea thermometers, these having been found to bring 

 up specimens of water whose turbid condition left no doubt that it had come 

 from the stratum immediately covering the soft ocean-bottom. The 

 Water-Bottle constructed on the Hydrographer' s plan is a simple strong 

 cylinder of brass, 26 inches long, and 2*3 inch in interior diameter, holding 

 about 60 oz. of water. In the disk which closes it in at each end there 

 is a circular aperture, into which a conical valve is accurately fitted. 

 "While this bottle is descending through the water with the Sound- 

 ing-Apparatus, the valves readily yield to the upward pressure, and 



