WILLIAM SIEMENS, F.R.S. 163 



\\ire, insulated with silk, is coiled in two or three layers upon the 

 brass tube, aa, as shown in section in Fig. (5, Plate 18. One end of 

 this wire is soldered to the tube : the other to a copper wire 

 insulated with gutta-percha and carried through a hole to the in- 

 terior. Over each end of the tube is drawn a piece of vulcanized 

 india-rubber pipe, b and )/, in the space between which the wire 

 is coiled. Over the whole is then drawn a larger india-rubber 

 pipe, iv, which, after being padded outside with hemp yarn, is 

 lashed tightly down by a stout binding wire. The gutta-percha- 

 covered wire forming the insulated end of the coil is placed 

 l>et ween the india-rubber pipes, b and c, which are so compressed 

 by the lashing as to close in upon it on all sides. The end of this 

 wire is soldered to one of the leading wires ; the other leading 

 wire being soldered to the top of the brass tube. The whole is 

 carried upon the end of the cable or sounding line, which contains 

 the leading wires. The reason for leaving the interior tube open 

 at both ends is to allow a free passage for the water through it, 

 in order to ensure the coil taking quickly the surrounding 

 temperature. 



Thermometer coils constructed in this manner are found to be 

 unaffected by any hydrostatic pressure to which they may be sub- 

 jected. As a test of their insulation, I subject all those intended 

 for deep-sea soundings to pressure under water before being finally 

 connected with the sounding lines. 



An instrument of this description was prepared, in 1869, for 

 the Dredging Committee, by which readings could be obtained to 

 one-tenth of a degree of Fahrenheit's scale, with the greatest 

 accuracy, in lowering the thermometer coil to the bottom of the 

 harbour. Unfortunately, however, accurate results could not be 

 obtained in deep water, because the motion of the ship rendered 

 the needle of the galvanometer employed too unsteady to allow of 

 dependence being placed upon its indications.* 



* A similar apparatus has been taken out on board H.M.'s steam-ship Chal- 

 . in her exploiing expedition, in which a Thomson marine galvanometer 

 - instituted for the more .simple instrument used on the previous occasion, 

 and which is better .suited for taking readings notwithstanding the motion of the 

 vessel. Considering that the zero position of the galvanometer has only to be 

 ascertained, the difficulty of operating with this instrument would not be con- 

 sidered great by those who are accustomed to electric observations on board ship, 

 although they ire still considerable to the uninitiated in this class of observations, 

 and renders the production of a more simple current detector a matter of con- 

 siderable interest. 



M 2 



