cHAP, Vi.] DEEP-SEA DREDGING. 243 
bags. Raw buffalo- and cow-hides are very strong, 
but they are apt to become offensive. When these 
are used it is necessary to punch holes here and there 
to let the water through or to leave the seams which 
are sewed with thongs a little open. Another bag 
which I have used frequently is made of sail-cloth, 
with a window of strong brass wire gauze let in on 
either side. Nothing, however, seems to me so good 
as strong cord netting. The water passes easily 
through and carries with it a large part of the fine 
mud, while enough mud is retained by the bread-bag 
lining in the bottom to give a fair sample of its 
contents. It may be said that many small valuable 
objects may be washed through the meshes of the 
upper part of the dredge along with the mud, and 
thus lost; but, on the other hand, if the bag be very 
close it is apt to get filled up with mud at once, and 
to collect nothing more. 
It is always well when dredging, at whatever 
depth, to ascertain the approximate depth with the 
lead before casting the dredge; and the lead ought 
always to be accompanied by a protected thermome- 
ter, for the subsequent haul of the dredge will gain 
greatly in value as an observation in geographical 
distribution if it be accompanied by an accurate note 
of the bottom temperature. For depths under 100 
fathoms the amount of rope paid out should be at 
least double the depth. Under thirty fathoms, where 
one generally works more rapidly, it should be more 
nearly three times. This gives a good deal of slack 
before the dredge if the boat be moving very slowly, 
and keeps the lip of the dredge well down; and if the 
boat be moving too quickly through the water, by 
R 2 
