Many of his letters are almost the equivalent of a scientific paper (there were as yet no scientific journals), and correspondents seem to have kept them because they were interesting.
Marami sa kanyang mga titik ay halos ang katumbas ng isang pang-agham ng papel (doon ay bilang pa walang pang-agham journal), at Koresponsal mukhang may iningatan ang mga ito dahil sila ay kagiliw-giliw.