800 OYSTERS, AND ALL ABOUT THEM. 



meters attached to " drop cylinders," used for obtaining 

 the specimens of water from the bottom, and six of those 

 cylinders were fitted at the office with mercurial thermo- 

 meters, inclosed within the spindle upon which the 

 cylinder moves, the bulb of the thermometer being a little 

 above the centre of the cylinder when closed on the lower 

 disk, and the graduated stem being exposed above the 

 top, thus allowing the temperature to be read within any 

 limits that would probably occur. 



. The cylinder is closed upon the lower 

 metal disk by means of a spiral brass spring, which also 

 holds the cylinder down firmly, thus preventing the escape 

 of the specimen. The spring acts with considerable force, 

 and we found that invariably the shock of the closure of 

 the cup was sufficient to break the mercurial column, and 

 prevent any reading of the thermometer. Attempts were 

 made on board the vessel to remedy the evil by diminishing 

 the strength of the spring, and by placing a rubber buffer 

 on the lower disk ; but we were unable to prevent leakage, 

 and subsequently the same difficulty was experienced at 

 the office. 



Owing to the failure of the thermometers in the water 

 cylinders, and the inability to obtain any apparatus, at so 

 short a notice, in time to be available for the season's work, 

 we were forced to use ordinary unprotected thermometers, 

 furnished by the Coast Survey Office, with corrections 

 established by experiments made previously and subse- 

 quently to the work of the party. The thermometers were 

 fastened to a lead, lowered to the bottom, and kept there 

 a sufficient time to acquire the temperature of the surround- 

 ing water. They were then hauled up as rapidly as possible 

 and the temperature read ; at the same time the temperature 

 of the air and water surface was noted. 



