o 
THE VOYAGE OF H.M.S. CHALLENGER. 
indicate the nature of the rock or other hard substance upon which the instrument had 
struck. In sounding in enclosed arms of the sea, such as the lochs of the west of 
Scotland, where the deposit is a soft mud, although the depths are usually under 100 
Fia 1. — The Cop Lead. 
A, ortlilury de*p-«e* lead ; B, in- 
verted hollow iron cone ; C, iron 
■pike ; D, tliiling iron dUc. 
A 
n 
Fio. 2. — Tlio Valve 
Sonnding I>ead. 
A, iron cylinder ; B, 
butterfly valve. 
Fios. 3, 4.— Buchanan’s Improved Sounding Lead. 
A and B, brass tube 1 inch (26'4 mm.) in diameter in two pieces, 
at lower end of the upper piece a shoulder C, with a thread 
screw, receives the corresponding shoulder D of the lower 
piece. The leaden weight M or N rests on the shoulder C. 
Wlien used, tube B is filled with a plug or cylinder of the mud, 
the upper part containing water. The plunger P is used to 
push out the plug of mud from B when the latter is unscrewed 
at D. Tlie weight M is 14 lbs. (6'4 kilogrammes), the weight 
N, 3 lbs. (1-4 kilogrammes). A comb valve may be fitted at 
the lower end of the tube if necessary (see L, Fig. 7). 
fathom.s, n mollification of this tube is desirable, so as to procure a section of the mud by 
plunging the tube deep into the deposit. Such a modification was devised by Mr. 
Buchanan and is represented in Figs. 3 and 4. 
Thr Hydra Sounding Machine, or the Baillie Sounding Machine, represented in the 
