Deep Sea Soundings. 347 



" Such was the apparent increase of the magnetic variation 

 as we proceeded eastward, on the parallel of 37° S., that the 

 effecting a landing on Tristan d'Acunha to test the actual 

 amount, free from any local disturbances of the ship, appeared 

 to me an essential step. Availing myself, therefore, of the 

 tranquil state of the weather, on the day of sighting it (12th 

 November), I effected a landing on the island, with the ne- 

 cessary instruments for settling the longitude, as well as the 

 variation of the compass, and the shore data at once confirmed 

 what had been indicated afloat, viz., that the variation has 

 doubled in amount since 1813, being now in that vicinity 20° 

 4' W., instead of 9° 51' W. 



" I took the opportunity of another calm day to ascertain 

 the temperature of the sea at 900 and at 1000 fathoms. At 

 both depths it proved the same, viz., 40° of Fahrenheit, whilst 

 near the surface it was 58°. At the same time I employed 

 means for tracing the depth to which the sun's rays pene- 

 trated, and found it to be 66 feet." 



As we considered the foregoing statement would have been 

 imperfect unless accompanied by particulars of this interest- 

 ing proceeding, contained in Captain Denham's letter to the 

 Hydrographer, Sir Francis Beaufort, it is with much satis- 

 faction that with his permission we are enabled to add to it 

 the following extract : — 



" I must not omit, even in this, to allude to the generous 

 offering to our expedition of 15,000 fathoms of sounding line 

 by Commodore M'Keever, of the United States Navy, whose 

 broad pendant was flying on board the Congress frigate at 

 Rio. He was not content with presenting me with books, 

 &c, but having observed that he had something in our wag, 

 sent me, the day before he sailed, 10,000 fathoms on one reel, 

 and 5000 on another, of most admirably adapted line for ex- 

 perimenting in deep deep-sea casts. Without compunction 

 as to ships' stores, I determined to hazard the 10,000 fathoms 

 (beautifully laid up, or grafted into one length) the very first 

 opportunity ; and we as assuredly did get to the bottom at 

 7706 fathoms, as not actually bringing up a sample can per- 

 mit me to say, for I and Lieut. Hutchison, in separate boats, 

 with our own hands, drew the plummet up 50 fathoms several 



