I GATHER from Mr. H. S. Rowell's letter published in NATURE for Decemebr 9 that, while interested in the subject of the flow of metals in shavings, he is not altogether familiar with the work that has already been done on the subject. In a comprehensive "Memoire sur le rabotage des metaux" (which cannot be so well known as I have hitherto believed) published more than forty years ago, M. H. Tresca investigated the question of the curling of shavings, both experimentally and mathematically, the actual flow of the metal (expressed by a coefficient de reduction) being especially selected for study under very varied conditions. the following quotation indicates only part of the scope of the work: “Cesphenomenes sone aussi ceux dans lesquels, pour la premiere fois, les metaux les plus durs, tels que I'acier, le fer, se comportent en realite comme le plomb, comme le savon, comme le savon, comme le cire, nous dirious presque comme les liquides, tant est complet le rapprochement que I'on doit faire entre les rides de nos differents copeaux et de veritables vagues de metal.”