BACKGROUND 



The bathyscaph was purchased by the U. S. Navy in 1958, 

 and it has since been considered to be an operational vehicle 

 capable of allowing its passengers to view any portion of the 

 deep ocean. This, however, is not strictly accurate. In 

 order to insure that the scientist will be able to make useful 

 visual observations on every dive, it is necessary to have a 

 reliable lighting system. 



At the time of its purchase, the bathyscaph utilized a high- 

 voltage, mercury-vapor lamp system. The lamps used 

 were specially manufactured for the bathyscaph by Phillips 

 in Belgium (fig. 1). Whereas the bulbs worked well in many 

 cases, they were not uniform in reliability. Some failed on 

 first trial and others failed after only short -duration use. 



There were apparently several causes for the failures, but 

 the most frequent failure was attributed to inability of the 

 bulb to withstand sudden changes in temperature. Since the 

 temperature in the deep oceans is near the freezing point, 

 the bulb casing was required to withstand a sudden transition 

 from a low ambient temperature to a high bulb temperature, 

 then again back to near 0°C when it was extinguished. 



Figure 1. Mercury vapor lamp employed in the original 

 lighting system on the bathyscaph. The steel casing was 

 used to provide a solid mount and to hold the reflector. 



