1 8 Papers from the Marine Biological Laboratory at Tortugas. 



If this form of apparatus is used, all sharp angles in the inlet tube should 

 be avoided, and it should be so arranged that the inrushing stream of water 

 spreads itself in a fan-shaped manner over the sides of the bulb, but I do 

 not consider that any form of exhausted glass flask is suitable even for 

 depths as small as 80 fathoms. 



In Jamaica no apparatus for obtaining deep samples was available, so 

 the primitive method of lowering a sterilized stoppered bottle with a string 

 tied to the stopper was employed. At the required depth the stopper was 

 pulled out until the bottle was nearly full and then allowed to fall back 

 in place. This method can only be used for very shallow depths, as the 

 pressure of the water at greater depths makes it impossible to withdraw 

 the stopper. A source of error is also introduced in that the inrushing 

 water passes in close proximity to the stopper and its attachment, and may 

 carry in bacteria which have adhered to them when passing through the 

 surface layers. 



Temperature records were obtained in the Bahamas by means of deep- 

 sea reversing thermometers specially made by Messrs. Negretti & Zambra 

 of London. They were tested up to a pressure of 3 tons to the square inch 

 at the National Physical Laboratory at Teddington, England, and a table 

 of temperature corrections was furnished for each instrument by the same 

 institution. These reversing thermometers differ from ordinary thermom- 

 eters in having a constriction and 8-shaped dilatation immediately above 

 the main bulb, with a somewhat large secondary bulb at the upper end of 

 the stem. The graduations are reversed, so that the lowest temperature 

 is marked near the top of the capillary portion. On turning the thermom- 

 eter upside down, the mercury thread breaks at the constriction and fills 

 the small bulb at the end of the capillary and also part of the capillary 

 itself. The thermometer is read in the reversed position, and when certain 

 corrections have been applied the temperature at which the thermometer 

 was reversed is recorded. The effect of the pressure of the water is avoided 

 by having the thermometer sealed in an outer glass case. The lower end 

 of this case is partially filled with mercury, in which the bulb of the thermom- 

 eter is immersed, thus allowing for rapid conduction of heat between the 

 mercury in the thermometer bulb and the surrounding water. An auxiliary 

 thermometer was sealed up in the same outer case as the reverser, so that 

 the temperature at which the actual reading was taken could also be re- 

 corded. In order to calculate the correction that must be applied to the 

 temperature registered by the reverser, three factors must be known: 



(a) Temperature of thermometer at moment of reading. 



(&) Kind of glass of which it is made. 



(c) Volume (expressed in degrees of the stem) of the secondary bulb and 

 the portion of the stem below the 0° graduation. 



Of these a is given by the auxiliary thermometer, and h and c were 

 engraved on the back of the stem of each reversing thermometer. All of 

 the thermometers were made of the glass known as Jena^*^ 16 III, and the 



