bubbles form in the brain or spinal cord, causing paralysis of
the legs, which is called divers' palsy, or the only trouble
which is experienced may be severe pains in the joints and
muscles. It is necessary, therefore, that he shall come up by
stages so as to decompress himself gradually and avoid danger.
The blood can hold about twice as much gas in solution as an
equal quantity of water, and when the diver is working in
shallow depths, up to, say, 30 ft, the amount of nitrogen
absorbed is so small that he can stop down as long as is
necessary for the purposes of the work, and can come up to the
surface as quickly as he likes without any danger. At greater
depths approximately the first half of the upward journey may
be done in one stage, and the remainder done by degrees, the
longest rest being made at a few feet below the surface.

The following table shows the time limits in accordance with
the latest British Admiralty practice; the time under the water
being that from leaving the surface to the beginning of the
ascent:--


TABLE No. l7.--DIVING DATA.

Stoppages in Total time
minutes at for ascent
Depth in feet. Time under water. different depths in minutes.

at 20 ft 10 ft

Up to 36 No limit - - 0 to 1