With the issue of the Third Part of the Third Volume, Mr Cantor completes his History of Mathematics, in accordance with the plan he sketched out for himself when he undertook the work. That the labour involved in collecting material and in reducing it to shape would be great, Mr Cantor doubtless well knew; but in all probability his most liberal estimate of the demands likely to be made upon his energies has been far exceeded; in any case, one can readily understand the feelings of satisfaction with which he writes the preface to the concluding volume.