Updated: Feb 7, 2020
If you want to talk about Observation, then Leonardo da Vinci is a pretty good place to start. Artists, by the very nature of what they are trying to do, need to be good observers, but Leonardo would surely be a shoo-in for 'Best in Breed'.
We were lucky enough to get to the Life in Drawing exhibition at the Queen's Galleries this summer, where we marvelled at his work.
It's a fabulous exhibition marking the 500th anniversary of the polymath's death using drawings that have been in the Royal Collection since the time of Charles II (and have been bound together even longer - since da Vinci's death in 1519).
What made Leonardo so special is that he didn’t just want to observe – he wanted to understand. He knew that effective Observation meant thinking about what you see. You notice evidence of this in so much of his work.
Take, for instance, his botanical drawings. Many of them started life as studies for a bigger painting (e.g. in preparation for doing Leda and the Swan), but he couldn't seem to help taking it a step further. While drawing the plants, he studied their structure to see how they worked, often making detailed notes about what he observed such as their form and habitat until he was as much scientist as artist.
As an aside, you might have noticed his famous mirror writing on the above drawing. He didn't always write this way. When his drawing was for (or to be seen by) other people, his writing would be the normal way round. It has been posited that, naturally left-handed, he did it this way so that he didn't damage his drawings by leaning his hand on them as he wrote.
In the same way that he studied botany in order to draw plants accurately, to draw people well he wanted to explore human anatomy. He used his knowledge of engineering and mechanics to work out how the bones, muscles, tendons etc. worked together; he was thus able to produce realistic poses.
He did this by observing closely - to the extent of attending autopsies - and then making detailed notes about how the body would work. His technical artistic skill meant that he could reproduce accurately what he was seeing. Interestingly, much of what he drew and surmised about how the body worked from attending over 30 autopsies have now been borne out by modern technology. For instance, he suggested how the heart might work in 1513, going so far as to make a working glass model of the aortic valve. His notes compare very favourably with what can be observed when watching an MRI scan.
Leonardo is credited with the first truly accurate depiction of the spine. Exceptional observation skills matched with superb draughtsmanship enabled him to draw its curvatures perfectly. He noted the various sections (e.g. cervical, coccygeal, lumbar, sacral, thoracic) and the different sizes of the spurs of bone on the vertebrae (transverse processes) as well as how the atlas and axis vertebrae fit onto the remaining vertebrae.
A major exception to his anatomical accuracy would be the female reproductive system. One of his drawings from 1509-10 depicts the cardiovascular system and principal organs of a woman. Like all effective Observation, that can include thinking about what you don't see, too. He wouldn't have had ready access to women to dissect (autopsies were often done on the bodies of executed criminals) so it was probably based on the drawings and notes he made when dissecting an old man in 1507-08. He used his memory of what he'd observed in the past (including dissections and observations of animals) to imagine what the female reproductive organs would be like. The diagonal lines and symmetry you see might be pleasing to the eye, but they are far from accurate. Those large ligaments are present in cows, because they carry the calf foetus under their body rather than in front as we do.
That just goes to show that even the brightest thinker can get it wrong if they don't have all the data. He made his best guess based on what information he had at the time and got it spectacularly wrong. Bear in mind that 15th/16th Century thought on reproduction would have been very different from what we have found to be the case - thinking it would be similar to the way plants worked. They also believed that the veins carried more than just blood, but the very spirit and soul of a person. Leonardo had wanted to know more about that in order to capture emotion in his painting. There is an argument for combining what you know (or can remember) and what you observe to propose a solution. However, even the most logical thought doesn't always lead to the right answer. Just consider all the space theories that have been proposed (and made sense given the data at the time) only to be completely debunked and rewritten when more accurate information became available.
Leonardo da Vinci intended to publish an anatomical treatise. Sadly, he died before that happened. It's interesting to consider what effects his drawings might have had on medical science if that volume had been available at the start of the 16th century - many of the things he observed weren't discovered by others until relatively recently.