86 THE AMERICAN MONTHLY [Mar 



fifteen band plates, running from 11,259 up to 56,297 ; the 

 nineteen band plates (of which he made more than any- 

 other series, and which are most often quoted) run from 

 11,259 up to 112,595 to the inch. A twenty band plate 

 was also made by M. Nobert, but the writer has never 

 seen one. It ran from the same initial (11,259) ap to 

 123,854. These figures are on the basis of the Paris 

 line being equal to 0.088,813,783 inch. Up to sometweny- 

 five or thirty years ago, M. Nobert had an absolute mo- 

 nopoly in this line, but about that time two or three Ameri- 

 cans devised ruling engines almost simultaneously — Pro- 

 fessor Rutherford, the astronomer, the late Professor 

 Henry Rogers, of Cambridge, and the late Henry Fasoldt, 

 chronometer maker of Albany, N. Y. The rulings, tech- 

 nically termed "gratings," of Mr. Rutherford are esteem- 

 ed all over the world aa superior to any other, and are 

 used in making the most delicate astronomical measure- 

 ments. Professor Rogers acquired a wonderful skill in 

 making rulings, and his plates are very highly prized by 

 those fortunate enough to possess them. They were never 

 made for sale. Some of th6 most wonderful of his rul- 

 ings are in the possession of Dr. W. J. Lewis. All of 

 the gratings sent out by Nobert, Rutherford, Rodgers 

 and those who have acquired the engines of the last- 

 named and made rulings with them, are accompanied by 

 "tables of corrections," which enable the observers who 

 use them as stage micrometers, to secure absolutely cor- 

 rect results. The late Mr. Fasoldt, refused to issue such 

 tables, claiming that they are unnecessary and that the 

 rulings are absolutely correct. The bands of rulings of 

 all the American artists in that line, are carried far be- 

 yond the power of the microscope to separate the lines, 

 and the distances between them are arrived at through 

 the spectrum which they present, the calculations being 

 based ou tiie wave lengths of light. Professors Rodgers 

 and Rutherford made gratings on speculum metal, and the 



