114 POPULAR SCIENCE MONTHLY.
decided unanimously to adopt the value advocated in 1884, and this is now the standard of the civilized world, a triumph of which Prof, Rowland is very proud.
Prof. Rowland's work in physics not only includes that pub- lished under his own name, but his influence is felt in the theses of his students who aspire to the degree of Doctor of Philosophy. One of the most notable of these was written by S. H. Hall, and describes a new phenomenon now known as the " Hall effect." The experiment leading to this discovery was described by Prof. Row- land in his lectures, and Mr. Hall was encouraged by his teacher to carry it out to a successful termination. The influence of Prof. Rowland's students in the recent revival of interest in physics, including electricity and magnetism, has been considerable, and the highest position in practical electricity available to an Ameri- can is held by Dr. Louis Duncan, President of the Society of Elec- trical Engineers, who is associated with Prof. Rowland and is one of his students.
Prof. Rowland has, with rare exceptions, devoted his time to pure research, and has never endeavored to accumulate a fortune. If he had patented his dynamo, which was finished ten years before Edison applied for a patent, his bank account would be large enough to enable him to perfect any idea he might con- ceive. Of late years Prof, Rowland has devoted himself princi- pally to the improvement of the apparatus for use in spectrum analysis. He has made three dividing engines for ruling the gratings used, each better than the one before it, and each pro- ducing gratings better than those of Mr. Rutherford, hitherto admitted to have been the best. At the present time, all the work of the world in spectroscopy requiring high dispersion is made with " Rowland's gratings."
Prof. Rowland has also invented the concave grating which can be used without lenses, and with which photographic work is best done. These results have been achieved principally by Prof. Rowland's skill as a mechanical designer, and his dividing en- gines have been constructed not only after his own design, but by processes invented by him and carried out under his own eye. So far nobody has been able even to copy the machines, although the processes have been freely described in his article Screw in the Encyclopsedia Britannica.
" Rowland's grating" is made by ruling parallel lines on a con- cave plate of what is known as speculum metal. This metal is an alloy of two parts copper and one part tin. The parallel grooves are made with a delicately adjusted diamond point. The machine on which the grating was made was manufactured after eighteen months' hard work by Theodore C. Schneider, the machinist at the university (a pupil of George M. Phelps, of Brooklyn), from the