The width of a dislocation in a simple cubic lattice is found to be only half of the original estimate, leading to a larger order of magnitude for the dislocation energy. The values for the energy are given as $6 \times 10^{-6}$, $2 \times 10^{-6}$, and $6 \times 10^{-6}$ for 02, 03, and 04, respectively. Expression (37) differs from Peierls's expression by replacing $(1-\sigma)$ with $2 \mathrm{~J}-\sigma$ and changing the form of the coefficient. The shear stress $T$ causes a uniform shear of the lattice through a small angle $\theta=T / \mu$, and this stress is equivalent to the mutual attraction of a pair of dislocations of unlike sign in the same glide plane at a distance of $2 \mathrm{~J} /(\mu \sigma)$. In an uncracked crystal, a pair of dislocations will callest if they are close together.The width of a dislocation in a simple cubic lattice is found to be only half of the original estimate, leading to a larger order of magnitude for the dislocation energy. The values for the energy are given as $6 \times 10^{-6}$, $2 \times 10^{-6}$, and $6 \times 10^{-6}$ for 02, 03, and 04, respectively. Expression (37) differs from Peierls's expression by replacing $(1-\sigma)$ with $2 \mathrm{~J}-\sigma$ and changing the form of the coefficient. The shear stress $T$ causes a uniform shear of the lattice through a small angle $\theta=T / \mu$, and this stress is equivalent to the mutual attraction of a pair of dislocations of unlike sign in the same glide plane at a distance of $2 \mathrm{~J} /(\mu \sigma)$. In an uncracked crystal, a pair of dislocations will callest if they are close together.