I believe one of the earliest "structural scientists" was Leonardo Da Vinci. Many people today consider him to be the model "Renaissance man",  who perfected his pictorial arts while at the same time dabbled in mechanical inventions, cartography, human anatomy and siege weaponry.  It may therefore be surprising to learn that when he was young, Da Vinci showed no natural aptitude for math or languages (especially Latin during a time when Latin was essential) - and he ended up working in a painter workshop more out of necessity. It was only much later in Milan after his apprenticeship that he began to dabble in science in a non-mathematical manner.  How can one be "scientific" without mathematics?  Da Vinci believed that to understand a thing, one must see it completely without bias.  Therefore, his scientific investigations sought to describe a phenomenon without quantitative theories but instead with meticulous visual reproductions. For example, to understand water eddies, he attempted to draw every visible shifting of water as they are formed:

"What causes the eddies of water" -  Notebooks of Leonardo Da Vinci

Through this painstaking work, the complex whirlpool and foam patterns are deconstructed to individual water paths, from which a general theory may arise. This purely descriptive endeavor is at the heart of structural science.  

Some centuries later Werner Heisenberg had this to say:

"The experiments of physics and their results can be described in the language of daily life. Thus if the physicist did not demand a theory to explain his results and would be content, say, with a description of the lines appearing on photographic plates, everything would be simple and there would be no need of an epistemological discussion. Difficulties arise only in the attempt to classify and synthesize the results, to establish the relation of cause and effect between them - in short, to construct a theory." 

 - from The Physical Principles of Quantum Theory - Werner Heisenberg

However, is it really possible to construct the experimental apparatuses to generate, record and then to recognize "lines appearing on photographic plates" without having some pre-formed theory?  Did Da Vinci really draw his eddies without any notion of what he was drawing?  Or perhaps at some point during his work, a theory arose in his mind, so that as he completed his lines of water, he completed them with an intact theory?  Unfortunately, I can no longer test this on myself through structural biology: my mind quickly interprets the computer generated blobs of electron density as idealized ribbons, screws and strands - with shapes corresponding to this or that amino acid residue - fitting everything into the standard theory.  Even at the beginning, before my first encounter with electron density, I had been heavily schooled in biochemical structures so that my mind was already prepared for what I was to see.  Recently, I showed some of these blobs from my published work to my aunt who had never been brainwashed by a scientific education:

mFo-DFc electron density map of a hairpin turn from a viral protein

However, to my great surprise and consternation, she responded with enormous disgust and fear - screaming that I was a very bad nephew for scaring her with this worm-like insect and that now she will have nightmares from seeing it...