150 



Messrs. Carpenter and Jeffreys on [Dec. 8, 



defray the expense of the messing of the scientific gentlemen composing 

 the Expedition. 



" I am, Sir, 



" Your ohedient Servant, 

 " To TV. Sharpey, Esq., M.D., " Vernon Lushington." 



Secretary of the Royal Society, 

 Burlington House." 



Equipment. 



1. The equipment of the 'Porcupine ' for the previous Expedition had 

 been found so complete and satisfactory that nothing more was considered 

 necessary to prepare her for the work of the present season than the over- 

 hauling of her gear, and the manufacture of new dredges, sieves, and other 

 apparatus, on the patternsof those whichhad already proved most serviceable. 

 We had the advantage of the same excellent Commander, now promoted to 

 the rank of Staff-Captain, with his able staff of Officers ; and we would take 

 this opportunity of again expressing our deep sense of obligation to them all 

 for their hearty co-operation in our scientific work, and for the unvarying 

 personal kindness by which our voyage was rendered a most agreeable one. 

 A considerable part of the Crew, also, consisted of the same steady and 

 experienced men. The Meteorological Department supplied eight of the 

 protected Miller-Casella Thermometers, including the two with the per- 

 formance of which we had been so thoroughly satisfied last year ; and we 

 usually employed one of these in conjunction with one that had not been 

 used in the previous Expedition. 



2. At the request of the Committee, Mr. Siemens undertook to devise 

 an Apparatus for testing the depth of Sea-water to which Light, or at least 

 the Actinic rays, can penetrate. The foundation of the apparatus which 

 he constructed for this purpose is a horizontal wheel with three radii, each 

 of them carrying a glass tube in which a piece of sensitized paper is sealed 

 up. The rotation of this wheel round a vertical axis brings each of the 

 tubes in succession out of a dark chamber in which it ordinarily lies, 

 exposes it to light in an uncovered space, and then carries it into darkness 

 again. This movement is produced by a spring ; but it is regulated by a 

 detent that projects from the keeper of an Electro-magnet, which is made 

 and unmade by the completion or breaking of a circuit that connects it with 

 a Galvanic battery. When the magnet is made, it lifts the keeper with its 

 projecting detent ; and this allows the wheel to be carried by the spring 

 through one-sixth of its rotation, whereby the first of the tubes is 

 brought out into the open space. There it remains until the circuit is 

 broken, whereby the magnet is unmade ; the keeper then falls, and the 

 wheel is allowed to move through another sixth of a rotation, so as to carry 

 on the tube into the dark chamber. A repetition of the making and un- 

 making of the magnet brings out the second tube, and shuts it up again ; 



