By John Muendel
Isis, Vol. 86, No. 3 (1995)
Introduction: When dealing with the history of overcoming friction in medieval machines, one cannot help but be struck by the investigations of Leonardo da Vinci. The Codice Atlantico, in particular, demonstrates that by measuring friction’s force on both horizontal and inclined surfaces, he was able to introduce the concept that the coefficient of friction is the ratio of its force to the weight or load applied (u = FIW). His quantitative experiments eventually allowed him to conclude that “every frictional body has a resistance of friction equal to one-quarter of its weight,” an approximation that is close to modem standards.’
In order to reduce such resistance, Leonardo went so far as to devise self-oiling systems for lubricating journals, or axle-ends, and a variety of roller- bearing arrangements, one of which had balls enclosed in a cage or retainer that anticipated recent schemes. A two-piece block that would prevent the axle from jumping out of the bearing was provided with metal bushings, or sleeves, made up of three parts copper and seven parts tin. The incorporation of this “mirror metal,” as he called it, indicates that Leonardo was also aware of low-friction metallic materials.
It would appear from these few illustrations that Leonardo’ s mechanisms were far ahead of the contemporary techniques of the late fifteenth and early sixteenth centuries. But however advanced his devices may have been, they do not present a complete picture of the effective remedies employed in his day for reducing friction in machines. His technological intuition allowed him to contrive the most sophisticated solutions to problems regarding this resistance, but it seems that he failed to delve thoroughly into the mundane details concerning lubrication. It is true that what is lacking might be found in his manu- scripts that have not as yet been uncovered. After all, since Leonardo was perennially in search of new pigments, varnishes, and gums for his paintings and decorative plates, he was aware of a variety of oils.
There are two factors, however, that argue against his thorough understanding of them as lubricants. First, Leonardo had a definite tendency to be sidetracked by problems immediately impinging upon his mind, so that larger projects remained unfinished. Second, his philosophical preoccupations prohibited a deeper examination of the more common techniques of his day. Influenced by the humanistic leanings of Roberto Valturio and Francesco di Giorgio Martini, a large number of his designs are either imaginative projections of antique models or pure mechanical abstractions that ultimately have no direct link to reality. Although he was intensely absorbed in nature and its actions, his vision of a universal science of inner microcosmic laws presupposed a scheme that limited his more scientifically inclined investigations. If Leonardo had found himself totally involved in contemporary techniques, he would have had to adjust his abstract speculations rather thoroughly. Theoretical views predominated in his thinking, and therefore his empirical pursuits were essentially disjointed.