As I was reading today an article from Nature I was wondering: Does anybody know what's the difference between article and letter in the Nature Journal?
The blog of Nature points out the following:
Articles are original reports whose conclusions represent a substantial advance in understanding of an important problem and have immediate, far-reaching implications.
Letters are short reports of original research focused on an outstanding finding whose importance means that it will be of interest to scientists in other fields.
Source: http://blogs.nature.com/nautilus/2009/12/difference_between_nature_arti.html