Freemasons
Just a few things about Freemasons:
1. The name.
In medieval times and the Renaissance, architecture was considered "the queen of sciences" as Renaissance-contemporaries put it. Architecture was the most prestigious profession, combining mathematics, engineering and art to create the most impressive objects mankind was capable of creating.
So, if you ran an organization in the Renaissance dedicated to science and research, you would naturally try to associate yourself with the "queen of sciences".
2. The culture.
The scientific community of the Renaissance was dominated by the philosophy of Hermeticism. One of the tenets of Hermeticism was that knowledge must be earned. You cannot simply give away knowledge to students. Instead, the knowledge is kept secret and is only revealed bit by bit once the student has proven mastery of what he has been taught so far.
(This is where the expression "hermetically sealed" comes from: Because Hermeticists were obsessed with secrecy.)
So, if you ran an organization in the Renaissance dedicated to science and research, you would naturally operate in secrecy, only revealing yourself to trusted members.