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II. Extract of a Letter to Admiral FiTzRov, F.R.S., from 

 Captain PULLEN of H.M.S. 'Cyclops/ dated Aden, March 

 16, 1858. Communicated by Admiral FiTzRov. Received 

 April 15, 1858. 



My first sounding for temperature at any depth, was in 32 13' N., 

 long. 19 5' W., where at 400 fathoms the minimum temperature 

 was 51-5, the surface at the time being 70. The water brought 

 up in the bottle was of greater density than we have since found it, 

 namely, 1031 at temp, of 70, whilst at the surface it was 1026. 

 Supposing that you will see all the registered depths, &c. sent to 

 Captain Washington, I do not enter into full detail here. The 

 next time, I sent two thermometers down at 500 and 800 fathoms ; 

 at the greater depth, 44*5 ; at the lesser, 50 was the minimum 

 temperature. But now I began to observe some alterations in 

 the indexes of the instruments, that of the maximum column 

 not returning to the surface in the same position in which it 

 stood on starting, viz. close to the mercury (brought to the sur- 

 face temperature by being kept sufficiently long in the water along- 

 side, and then compared with the deck-thermometer in constant 

 use for that observation) . Now I know from former experience that 

 these indexes will shift by shaking the instrument, and with much 

 less force than is frequently communicated to it by a shake of the 

 line, on its passing up and down. From this we may infer that the 

 minimum index also moves, how much it is impossible to say. And 

 on looking over the results obtained during the voyage, I find that 

 but few of the maximum indexes have come in standing at the point 

 they started with. I therefore draw your attention to the fact, that 

 such remedy may be applied as will obviate the defect. I have 

 found another fault in thermometers before now (but then it was at a 

 low temperature, and not Six's self- registering instrument that was 

 employed). During my second winter at Fort Simpson, I, every three 

 hours throughout twelve of the twenty- four, registered twenty-one 

 thermometers, eighteen of Adie's and three of Negretti's, on glass 

 scales. I never found Adie's at any temperature to differ more than 

 a degree and a half from each other. Negretti's, when they ranged 

 low, say twenty below zero, I have found twenty, eighteen, and 



