put wool,
saturated with oil, in their ears. Others hold in their mouth a piece of
sponge soaked in oil, which they renew every time they descend. It is
doubtful, however, whether these expedients are beneficial. The men who
dive in this primitive fashion take with them a flat stone with a hole
in the centre; to this is attached a rope, which is secured to the
diving boat and serves to guide them to particular spots below. When the
diver reaches the sea bottom he tears off as much sponge within reach as
possible, or picks up pearl shells, as the case may be, and then pulls
the rope to indicate to the man in the boat that he wishes to be hauled
up. But so exhausting is the work, and so severe the strain on the
system, that, after a number of dives in deep water, the men often
become insensible, and blood sometimes bursts from nose, ears and mouth.

_Early Diving Appliances._--The earliest mention of any appliance for
assisting divers is by Aristotle, who says that divers are sometimes
provided with instruments for respiration through which they can draw
air from above the water and which thus enable them to remain a long
time under the sea (_De Part. Anim._ 2, 16), and also that divers
breathe by letting down a metallic vessel which does not get filled with
water but retains the air within it (_Problem._ 32, 5). It is also
recorded that Alexander the Great made a descent into the sea in a
machine called a _colimpha_, which had the power of keeping a man dry,
and at the same time of admitting light. Pliny also speaks of divers
engaged in the strategy of ancient warfare, who drew air through a tube,
one end of which they carried in their mouths, whilst the other end was
made to float on the surface of the water. Roger Bacon in 1240, too, is
supposed to have invented a contrivance for enabling men to work under
water; and in Vegetius's _De Re Militari_ (editions of 1511 and 1532,
the latter in the British Museum) is an engraving representing a diver
wearing a tight-fitting helmet to which is attached a long leathern pipe
leading to the surface, where its open end is kept afloat by means of a
bladder. This method of obtaining air during subaqueous operations was
probably suggested by the action of the elephant when swimming; the
animal instinctively elevates its trunk so that the end is above the
surface of the water, and thus is enabled to take in fresh air at every
inspiration.

A certain Repton invented "water armour" i