Measurements of fragment-production cross sections have been made with $^{18}\mathrm{O}$ projectiles of 1.7 GeV/nucleon incident upon targets of Be, C, Al, Ti, Cu, Sn, W, Pb, and U. We have found that the enhancement with high-$Z$ targets of cross sections for certain fragments agrees both in magnitude and ${Z}_{T}$ dependence with the predictions of the electromagnetic-dissociation process, which are based upon the known photonuclear cross sections and classical relativistic virtual-photon theory. We have found as well that factorization of the cross sections for nuclear processes is valid to an accuracy of better than 4%.NUCLEAR REACTIONS Be($^{18}\mathrm{O}$,$X$), $C(^{18}\mathrm{O},X)$, Al($^{18}\mathrm{O}$,$X$), Ti($^{18}\mathrm{O}$,$X$), ${\mathrm{C}\mathrm{u}(}^{18}$O,$X$), Sn($^{18}\mathrm{O}$,$X$), W($^{18}\mathrm{O}$,$X$), Pb($^{18}\mathrm{O}$,$X$), U($^{18}\mathrm{O}$,$X$), $X=^{6}\mathrm{Li} \mathrm{to} ^{18}\mathrm{F}$, $E=1.7$ GeV/nucleon; measured fragment-production cross sections; deduced electromagnetic-dissociation cross sections, ${Z}_{T}$ dependence, factorization parameters. $^{18}\mathrm{O}$ fragment-production cross sections, electromagnetic dissociation, factorization, relativistic heavy ions.