5 ▁and ▁ 1 9 3 8 , ▁respectively , ▁contin ually ▁adv ancing ▁T EM ▁design . ▁ ▁Research ▁continued ▁on ▁the ▁electron ▁mic ros cope ▁at ▁S iem ens ▁in ▁ 1 9 3 6 , ▁where ▁the ▁aim ▁of ▁the ▁research ▁was ▁the ▁development ▁and ▁improvement ▁of ▁T EM ▁imag ing ▁properties , ▁particularly ▁with ▁regard ▁to ▁bi ological ▁spec im ens . ▁At ▁this ▁time ▁electron ▁micro scop es ▁were ▁being ▁fabric ated ▁for ▁specific ▁groups , ▁such ▁as ▁the ▁" EM 1 " ▁device ▁used ▁at ▁the ▁UK ▁National ▁Phys ical ▁Labor atory . ▁In ▁ 1 9 3 9 , ▁the ▁first ▁commercial ▁electron ▁mic ros cope , ▁p ict ured , ▁was ▁installed ▁in ▁the ▁Physics ▁department ▁of ▁I G ▁Far ben - W er ke . ▁Further ▁work ▁on ▁the ▁electron ▁mic ros cope ▁was ▁ham per ed ▁by ▁the ▁destruction ▁of ▁a ▁new ▁labor atory ▁constructed ▁at ▁S iem ens ▁by ▁an ▁air ▁ra id , ▁as ▁well ▁as ▁the ▁death ▁of ▁two ▁of ▁the ▁research ers , ▁Hein z ▁Müller ▁and ▁Fried rick ▁Kra use ▁during ▁World ▁War ▁II . ▁ ▁Further ▁research ▁After ▁World ▁War ▁II , ▁Rus ka ▁res umed ▁work ▁at ▁S iem ens , ▁where ▁he ▁continued ▁to ▁develop ▁the ▁electron ▁mic ros cope , ▁producing ▁the ▁first ▁mic ros cope ▁with ▁ 1 0 0 k ▁magn ification . ▁The ▁fundamental ▁structure ▁of ▁this ▁mic ros cope ▁design , ▁with ▁multi - stage ▁beam ▁prepar ation ▁opt ics