Tomorrow (the fifth) is an important memorial of someone who is all too often forgotten: Nicholas Steno, also called Niels Stensen. Steno is one of the most stunning scientific minds in history, and a truly saintly person; I have an old post giving some of the highlights of his life. Strictly speaking, Steno's memorial is only officially celebrated in certain parts of Europe, since he has only been beatified; but it seems worthwhile to mark the day.
It's also worth pointing out, since it is often overlooked, that Steno could plausibly lay claim to being the person who did the work of showing that Descartes was wrong about the pineal gland, at least in the sense that he showed that Descartes made false anatomical assumptions about the pineal gland and argued that, in fact, we knew very little about the brain at all. (He also, and more obviously, showed that Descartes was wrong, and Harvey right, about the heart. He was, however, a very great admirer of Descartes, and explicitly defends him from hasty condemnations, insisting that they overlook the beauty of Descartes's work; in science it really is sometimes the case that refutation is the greatest form of flattery.) You can read a French version of the work in which he does this thanks to Gallica. Their format requires a lot of patience to navigate, but it's worth a perusal, if only to read a lecture in seventeenth-century neuroscience by perhaps its foremost practitioner, laying out the structure of the brain in a way that, given the tools of the time, could only be done by a man with an almost flawless surgical hand, expressing doubts about this whole notion of 'animal spirits', carefully marking off the things not known from things known.
There's an old joke about Aristotle -- how on Monday he wrote the Physics, but getting tired of that subject, wrote the Poetics on Tuesday; figuring that he'd done enough of that for a while, catalogued all the Greek constitutions on Wednesday; then, deciding that was too mundane, wrote the Metaphysics on Thursday; realized he'd forgotten to write something for Nichomachus, so wrote the Nichomachean Ethics on Friday; and decided to take a break from it all on Saturday by writing all the logical works. It's not a very funny joke, but it gives a slightly funny caricature of how stunning -- one might almost say shocking -- it is that a single man was able to do so much even in a lifetime; and everyone always has the same reaction to Steno, whose life is not all that much less stunning than someone proving Harvey right about the heart on Monday, founding the modern understanding of the glands on Tuesday, proving Descartes wrong about the brain on Wednesday, then settling down for the easy tasks of inventing paleontology on Thursday and geology on Friday before he takes the weekend off to become a saint. It's a funny caricature, but, allowing for all the exaggeration, it's uncomfortably like its original.