Following his education in Giessen , he took postdoctoral fellowships in Paris ( 1851-52 ) , in Chur , Switzerland ( 1852-53 ) , and in London ( 1853-55 ) , where he was decisively influenced by Alexander Williamson . Following his education in Giessen , he took postdoctoral fellowships in Paris ( 1851 â `` 52 ) , in Chur , Switzerland ( 1852 â `` 53 ) , and in London ( 1853 â `` 55 ) , where he was decisively influenced by Alexander Williamson .