On the other hand; modern spectroscopic techniques are capable of reporting on molecular details, however, isolating the comparatively tiny interfacial signal from that of the bulk is a general challenge affecting the spectroscopic community. In addition, spectroscopists must account for the sometimes significant interactions of pump and probe pulses with the solid. In some cases, these interactions can be harnessed to amplify interfacial signal. Despite these challenges, our ability to measure the molecular properties of solid-liquid interfaces continues to improve. Some of the first insight into interfacial electrostatics were derived from measurements of interfacial differential capacitance, quantifying the change in solid surface charge with applied voltage, and electrocapillarity, measuring the surface tension of electrode-electrolyte solution interfaces. These measurements led to the development of the concept of an electric double-layer (EDL), which persists today as a cornerstone of our microscopic understanding of solid-liquid interfaces.