243 



the greatest depth which the motion of the vessel permitted them 

 to reach. They reserve for a future report their observations on the 

 temperature and moisture of the air, as well as the results of two 

 experiments on the quantity of carbonic acid contained in the air on 

 the Mediterranean and Red Seas. 



The instruments employed in the observations here described 

 were as follows : 



(1.) Four thermometers which had been carefully compared at 

 the Kew Observatory previous to the authors' departure. At Bom- 

 bay they repeated the determination of the zero-point and of an- 

 other standard point, and found that the thermometers had not 

 varied. 



(2.) A dipping apparatus constructed by Mr. Adie. This appa- 

 ratus, which held 5 or 6 litres, was furnished with two valves, so 

 arranged that as it descended the water passed freely through, but 

 as soon as a commencement was made of drawing it up the valves 

 closed and rendered it water-tight. The authors assured themselves 

 that the temperature of the enclosed water did not sensibly change 

 during the process of drawing it up. 



(3.) An areometer from Mr. T. G. Greiner at Berlin. This in- 

 strument permitted the specific gravity to be read off directly to 

 three places of decimals, and the fourth could be supplied by estima- 

 tion. 



To render the observations of specific gravity comparable with one 

 another, it was necessary to reduce them to a common temperature, 

 which occasioned some difficulty, as the exact expansion of sea- 

 water between the limits 20 and 25 C. was not accurately known. 

 By means of a delicate voluminometer, constructed for the purpose 

 by M. Geissler of Berlin, the authors determined the expansion to be 

 0-000271 for 1 C. For distilled water Halstrom had found 0-000219. 

 Another set of more direct experiments, made at Bombay, gave for 

 the expansion of sea-water 0'000337. The difference between this 

 value and the preceding the authors refer to a change of volume of 

 the voluminometer itself, and they prefer the latter, which accord- 

 ingly they use in their reductions. 



The authors then give tables of the results of their observations, 

 which are followed by some general remarks. 



2 B2 



