December 6, 1901.] 



SCIENCE, 



871 



free from periodic and other errors, and 

 upon this problem a vast amount of thought 

 and experiment had already been expended. 



Rowland's solution of it was character- 

 istic of his genius ; there were no easy ad- 

 vances through a series of experiments in 

 which success and failure mingled in vary- 

 ing proportions ; ' fire and fall back ' was 

 an order which he neither gave nor obeyed, 

 capture by storm being more to his mind. 

 He was by nature a mechanician of the 

 highest type, and he was not long in devis- 

 ing a method for removing the irregularities 

 of a screw, which astonished everybody by 

 its simplicity and by the all but absolute 

 perfection of its results. Indeed, the very 

 first screw made by this process ranks to- 

 day as the most perfect in the world. But 

 such an engine as this might only be worked 

 up to its highest eflBciency under the most 

 favorable physical conditions, and in its in- 

 stallation and use the most careful atten- 

 tion was given to the elimination of errors 

 due to variation of temperature, earth tre- 

 mors and other disturbances. Not content, 

 however, with perfecting the machinery by 

 which gratings were ruled, E-owland pro- 

 ceeded to improve the form of the grating 

 itself, making the capital discovery of the 

 concave grating, by means of which a large 

 part of the complex and otherwise trouble- 

 some optical accessories to the diffraction 

 spectroscope might be dispensed with. Call- 

 ing to his aid the wonderful skill of Brashear 

 in making and polishing plane and concave 

 surfaces, as well as the ingenuity and pa- 

 tience of Schneider, for so many years his 

 intelligent and loyal assistant at the lathe 

 and work-bench, he began the manufacture 

 and distribution, all too slowly for the anx- 

 ious demands of the scientific world, of 

 those beautifully simple instruments of pre- 

 cision which have contributed so much to 

 the advance of physical science during the 

 past twenty years. 



While willing and anxious to give the 



widest possible distribution to these grat- 

 ings, thus giving everywhere a new impetus 

 to optical research, Rowland meant that the 

 principal spoils of the victory should be his, 

 and to this end he constructed a diffraction 

 spectrometer of extraordinary dimensions 

 and began his classical researches on the 

 solar spectrum. Finding photography to 

 be the best means of reproducing the deli- 

 cate spectral lines shown by the concave 

 grating, he became at once an ardent stu- 

 dent and, shortly, a master of that art. 

 The outcome of this was that wonderful 

 * Photographic Map of the Normal Solar 

 Spectrum,' prepared by the use of concave 

 gratings six inches in diameter and twenty- 

 one and a half feet radius, which is recog- 

 nized as a standard everywhere in the 

 world. As a natural supplement to this he 

 directed an elaborate investigation of abso- 

 lute wave-lengths, undertaking to give, 

 finally, the wave-length of not only every 

 line of the solar spectrum, but also of the 

 bright lines of the principal elements, and 

 a large part of this monumental task is al- 

 ready completed, mostly by Rowland's pu- 

 pils and in his laboratory. 



Time will not allow further expositions of 

 the important consequences of his invention 

 of the ruling engine and the concave grating. 

 Indeed, the limitations to which I must 

 submit compel the omission of even brief 

 mention of many interesting and valuable 

 investigations relating to other subjects 

 begun and finished during these years of 

 activity in optical research, many of them 

 by Rowland himself and many of them by 

 his pupils, working out his suggestions and 

 constantly stimulated by his enthusiasm. 

 A list of titles of papers emanating from the 

 Physical Laboratory of the Johns Hopkins 

 University during this period would show 

 somewhat of the great intellectual fertility 

 which its director inspired, and would 

 show, especially, his continued interest in 

 magnetism and electricity, leading to his 



