174 Mr. J. T. Bottomley. On a Gravity [June 19, 



Fig. 1 shows the cell in plan, and fig. 2 the same in section. The 

 outer containing vessel is a large shallow tray of wood, very strong, 

 but quite roughly made, and lined with sheet lead. The tray is 



Fro. 2. 



3| inches deep, and with this small depth the lead can be beaten in, 

 and autogenous soldering is unnecessary. The lead tray is very care- 

 fully varnished with spirit varnish, several coats being applied ; and 

 on the bottom of it is laid a thin sheet of copper (0'2 millim. thick), 

 or rather several sheets thoroughly connected together, as I have not 

 been able to obtain a single sheet of copper large enough for my 

 purpose. The copper sheet, varnished on the lower side, is attached 

 in many places to the lead lining of the trough by soldered slips of 

 copper, the solderings being thoroughly coated with varnish or marine 

 glue. This copper sheet forms the copper plate of the Darnell's cell. 

 The zinc of the cell consists of four of an unusually large size 

 (56 centims., 22 inches square) of the gridiron zincs used in Sir William 

 Thomson's well-known tray Daniell, which is largely employed at most 

 of the submarine telegraph stations in connexion with the Siphon 

 Recorder, and is a modification of the constant Daniell's battery 

 described " Proc. Roy. Soc.," 1871, p. 253. These gridiron zincs rest 

 on small blocks of wood at the four corners of each, and they are con- 

 nected together by strong copper slips at the corners, and by means 

 of two diagonals of thick copper rod which are soldered at the out- 

 lying corners and at the four meeting corners in the middle of the 

 square. 



FIG 3. 



Very powerful pairs of electrodes are soldered on at each of the 

 four corners of the cell, though only one of these pairs is shown in 

 the diagram at D. These electrodes are formed of flexible copper 



