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Murray wrote

We know that he was baptised on January 9, 1828.  We can safely assume he was born late in 1827.  I have found a secondary source reference to 1827 but with no actual birth date.  Here is a link to the date of baptism and some brief biological information.  (Page 291 if the full link does not work).

Thanks for the links. It seems that Johnson lived through a very significant period in the history of CN. After his death developments were mainly the creation of tables -  first by human computers and later electronic ones. Off the top of my head I do not know when radio time signals were first broadcast and RDF first used but maybe Johnson was aware of these technigues?

He was  a subject of four monarchs, including one who reigned for 63 years.

I will add the information to my notes. I must start searching fo some of Johnson's other books. Ideally hard copy but I will probably have to be satisfied with pdfs.