n 4 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 

 Encyclopedia 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 



