▁side ▁vent ures ▁was ▁also ▁early ▁div ing ▁bell ▁development , ▁used ▁to ▁recover ▁material ▁from ▁ship w re cks , ▁upon ▁challenge ▁by ▁a ▁Swedish ▁expert ▁Ros enberg ▁that ▁it ▁would ▁be ▁impossible ▁to ▁develop ▁technology ▁to ▁access ▁a ▁designated ▁ship w reck . ▁Hence ▁he ▁invent ed ▁a ▁div ing ▁bell ▁built ▁of ▁t inned ▁co pper ▁with ▁space ▁for ▁a ▁crew ▁of ▁ 2 - 3 ▁persons . ▁In ▁ 1 8 2 5 , ▁the ▁bell , ▁equ ipped ▁with ▁comp ass ▁and ▁methods ▁of ▁communication ▁to ▁the ▁surface , ▁successfully ▁div ed ▁down ▁to ▁ 2 5 ▁ ells ▁with ▁L j ung ström ▁and ▁an ▁assistant ▁on ▁board , ▁" to ▁the ▁a we ▁of ▁the ▁local ▁society , ▁much ▁of ▁which ▁was ▁assemble d ▁for ▁the ▁demonstr ation ." ▁ ▁L j ung ström ▁went ▁on ▁to ▁author ▁a ▁book ▁present ing ▁technology ▁and ▁ideas ▁for ▁a ▁private ▁sector ▁of ▁under water ▁div ing ▁in ▁Sweden , ▁which ▁was ▁until ▁then ▁still ▁strictly ▁subject ▁of ▁authorities ▁in ▁the ▁form ▁of ▁public ▁div ing ▁companies . ▁ ▁Tow ards ▁the ▁ 1 8 3 0 s ▁he ▁re located ▁to ▁Saint ▁Petersburg , ▁attached ▁to ▁the ▁Evangel ical ▁Luther an ▁Church ▁of ▁Saint ▁Kat arina , ▁where ▁also ▁Im manuel ▁Nobel ▁( 1 8 0 1 – 1 8 7 2 ) ▁was ▁active ▁and ▁with ▁whom ▁he ▁may ▁have ▁collabor ated ▁in ▁under water ▁invent ions . ▁ ▁Upon ▁return ▁to ▁Sweden ▁towards ▁the ▁end ▁of