Giovanelli is distinguished for his theoretical and experimental contributions to astrophysics in the fields of solar physics, radiative transfer and astronomical optics. His theoretical contributions comprise the two-column theory of the chromosphere, the electromagnetic origin of solar flares and of runaway electrons in plasmas, basic ideas on the emission of radiation from high temperature atmospheres which instigated general studies of three dimensional radiative transfer. He is also responsible for the method of quantitative chemical analysis by diffuse reflection spectrophotometry, which is important in studies of the rapid pigment changes in bacterial cells and of the influence of diffusion on the resolving power of photographic emissions. Giovanelli early drew attention to the significance of electromagnetic phenomena that accompany the growth of sunspots in the formation of solar flares and this stimulated much of the observational and theoretical work, to which he has also contributed, on chromospheric disturbances, during the last 15 years. Recently he has developed greatly improved methods of observing the velocity and magnetic field distributions in the photosphere and chromosphere and in solar disturbances which are extremely relevant to the interpretation of many phenomena that occur in the earth's upper atmosphere that have been the subjects of world-wide study. The improved methods have depended upon his development of new optical instruments, in particular a 1/8° filter, with which to obtain photographs that reveal the distribution of the velocities and magnetic fields at various levels in the solar atmosphere.