448 



SCIENCE. 



[N. S, Vol. VII. No. 170. 



life the most distinguishing characteristics 

 of Professor Eogers, as a student and 

 teacher of science, were his indomitable 

 perseverance, industry, care, patience and 

 accuracy. Beginning as a teacher of pure 

 mathematics, he passed naturally into 

 specialization in astronomy and its allied 

 neighbors, mechanics and physics. His de- 

 light was minute measurement, with ac- 

 curacy to the last decimal place that patient 

 industry could render attainable. He 

 sought accuracy not merely for the secur- 

 ing of the best practical results, but because 

 he had a veritable passion for its pursuit. 

 The first time that the present writer came 

 into contact with him was at the Boston 

 meeting of the Scientific Association in 

 1880, when he gave the outcome of an 

 elaborate comparison between the standard 

 French meter and the imperial yard, the 

 uncertainty being in the value of the digit 

 occupying the place of ten-thousandths of 

 an inch. Another result almost identical 

 with the first was reported in 1882 at 

 Montreal as the outcome of new measure- 

 ments, the meter being equivalent to 

 39.37015 inches under standard conditions. 

 Still another was given a year later at Min- 

 neapolis, 39.37027 inches. At Philadel- 

 phia, in 1884, he announced a re-examina- 

 tion of his data, with the expression of his 

 conviction that this result was a little too 

 high, but that the true value could not be 

 less than that given at Montreal. At 

 Buffalo, in 1886, 39.37020 inches was given 

 as a new determination. In 1893, as the 

 mean of eleven determinations, he gave 

 39.370155 inches. This may be taken as a 

 final value. It has been subjected to two 

 or more revisions by him since 1893, but 

 with no appreciable change as the result. 

 All physical measurements are necessarily 

 only approximate. There are probably 

 very few of them that have been made 

 with a degree of exactitude superior, or 

 even equal, to this one. 



The scientific papers published by Pro- 

 fessor Rogers are about seventy in number. 

 The first, which appeared in 1869, was forty- 

 five pages in length, and related to the de- 

 termination of geographical latitude from 

 observations in the prime vertical. He was 

 at this time about thirty-seven years of age, 

 and still connected with Alfred University, 

 where the facilities for research were very 

 limited. Under his direction in 1865 Alfred 

 Observatory was built and subsequently 

 equipped. His activity as a scientific 

 worker was much stimulated after his con- 

 nection with the Harvard Observatory be- 

 came established. During the sixteen years 

 of his residence in Cambridge he published 

 forty scientific papers, most of which re- 

 lated to practical astronomy, such as the 

 determination of star places, the calcula- 

 tion of ephemerides, the study of the errors 

 of instruments, the construction of star 

 catalogues from all known data, etc. In- 

 cluded in such work as this the study of 

 the microscope as an instrument of pre- 

 cision was naturally developed, and the 

 methods of securing accurate rulings for 

 micrometers became a subject for the appli- 

 cation of industry. This led Professor 

 Eogers into the study of physical standards 

 of length, and the construction of ruling 

 machines, regarding which he made him- 

 self a generally recognized authority. The 

 articles on ' Measuring Machines ' and 

 ' Ruling Machines ' in the new edition of 

 Johnson's Cyclopedia were written by him. 

 In all accurate measurements of length 

 the recognition of the temperature at which 

 they are made is a matter of prime impor- 

 tance, since a slight variation in tempera- 

 ture produces a measurable change of 

 length. The recognition of this fact caused 

 Professor Rogers to enter into an extended 

 study of the limits of precision in ther- 

 mometry, of radiation, and of coeflBcients of 

 expansion. This continued to be his chief 

 study during the closing years of his life. 



