In 1953, biologists Francis Crick and James Watson discovered the structure of DNA. Crick wrote a letter to his 12-year old son Michael describing the discovery. The son recently auctioned the letter at Christie's in New York City for $6 million. Here's a transcription of the first page:
19 Portugal Place Cambridge
19 March ’53
My Dear Michael,
Jim Watson and I have probably made a most important discovery. We have built a model for the structure of de-oxy-ribose-nucleic-acid (read it carefully) called D.N.A. for short. You may remember that the genes of the chromosomes — which carry the hereditary factors — are made up of protein and D.N.A.
Our structure is very beautiful. D.N.A. can be thought of roughly as a very long chain with flat bits sticking out. The flat bits are called the “bases”. The formula is rather
You can view the other pages and read the transcriptions, including Crick's handwritten diagrams of DNA, at the link.