As we have seen, it was clearly Guyton's intention, in 1808, to supply details of his improved platinum pyrometer, and he did submit a drawing of the instrument at the meeting of the Class in December 1810. It would seem that on that occasion he did not supply those details which are to be found in the fourth, unpublished, part of the ‘Essay’. The existence of a text fit to be sent to the printer, and the execution of a drawing (...) relating to the improved version of his platinum pyrometer, might be taken as evidence that Guyton intended to publish. His paper of 1810 did not appear until 1814, however, so that publication of the fourth part of the ‘Essay’ could scarcely have occurred until 1815 or later. Guyton probably hoped to be able to read it to the Class of Physical and Mathematical Sciences before publishing it in the Annales de Chimie, but his death on 2 January 1816 robbed him of the opportunity. (shrink)