470 The Commercial Products of the Sea. 



used for works under water in which the head of the diver 

 has to be kept upright (repairing ships, for instance), while 

 the mask is adopted for researches and examinations on 

 the sea bottom. 



A great advantage of this arrangement is that the diver 

 has always a certain reserve quantity of air in the regulator, 

 so that a falling off in the supply of air is not connected 

 with immediate danger or disadvantages for him. The 

 supply of air to the diver is regulated by a peculiarly con- 

 structed valve, by means of which the pressure, under which 

 the air is supplied, corresponds always with the depth of 

 the water in which the diver is acting. 



The air coming from the diver is not allowed to mix 

 with the fresh supply of air, but escapes to the surface 

 through a side-port closed by an india-rubber valve. The 

 diver is able to increase or diminish his specific weight by 

 simply altering the volume of air between his dress and 

 body ; and, in this manner, it is in his power to ascend or 

 descend as he likes. 



Amber constitutes an important article of trade on the 

 Dantzic coast, and it is exported, both in pieces and 

 worked, to Austria, France, and the East. This trade is 

 completely in the hands of a few families. The principal 

 deposit is found on the coast of Samland, from Pillau to 

 Gross Hubnicken. In this space of three miles the ex- 

 traction of amber is farmed by the Government. The 

 annual yield is about 200,000 Ibs. The produce is classed 

 into six qualities, according to the size and quality of the 

 pieces. 



The largest piece known is 13! inches long by eight and 

 a half inches wide, and three to six inches thick. It weighs 

 13 \ Ibs., and is in the Berlin Museum. At the Great 

 Exhibition of 1851, two pieces were shown, for beauty and 



