How does one fluid body become two? At what point do the two separate, but still hold together? For Sidney Nagel, it was is not enough just to ask these questions, it was necessary to see exactly what this moment looks like. This image, titled "Two-Fluid Snap Off" was created by Nagel, a professor in the department of physics at the University of Chicago. It shows one drop of glycerol breaking apart inside the surrounding oil (Polydimethylsiloxane). Nagel writes that since the viscous fluids were both transparent, it was difficult to show the details of the shape at the breaking point. Using customized dark-field lighting, he was able to make even the narrowest point of contact clearly visible. High speed strobe photography made it possible to catch the breaking drop phenomena in focus at a high level of magnification, when it was only visible for the briefest instant. Nagel writes: "Scientific photography has the potential to cross boundaries of human emotion and intention; it can display as well as document nature. It allows the viewer to witness in wonder as well as understand in quantitative detail some of the marvels that are concealed from ordinary perception." This image is part of the National Academy of Sciences art collection and is featured in a new book, Convergence, highlighting that collection.