Berlin, Königl. Akad. d. Wissenschaften, 1866. Uncut in orig. printed wrappers in ""Monatsbericht der Königlichen Preussischen Akademie der Wissenschaften zu Berlin"", Sept., October 1866. Pp. 595-655. Weierstrass' paper: pp.612-625. Kronecker's paper: pp. 597-612
Both papers first edition. Weierstrass is considered the most importen nineteenth-century german mathematician after Gauss and Riemann.