If you have access through a university library, HathiTrust holds high-resolution scans of the original 1860 German edition ( Elemente der Psychophysik ) and the 1912 English translation. You can download PDFs of individual pages or entire books if you are a partner institution member.
"Elements of Psychophysics" by Gustav Fechner is a seminal work that laid the foundation for the field of psychophysics. First published in 1860, this book is a comprehensive and systematic treatment of the relationship between physical stimuli and the sensations they produce. Fechner, a German philosopher and physicist, is considered the founder of psychophysics, and this book is a testament to his innovative and rigorous approach to understanding the mind-body problem. elements of psychophysics fechner pdf
This insight led to the (often misattributed to Weber, but formalized by Fechner): Sensation increases proportionally to the logarithm of the stimulus intensity. If you have access through a university library,