44 ANNUAL KECORD OF SCIE];JCE AND INDUSTRY. 



common operations in multiplication, division, etc. It is a 

 foot in length by half as much in height and width, weighs 

 twenty pounds, and contains less than 400 pieces, less than 

 75 of which are working parts. It takes numbers up to nine 

 decimal places. Its mechanism is simple, strong, and dura- 

 ble ; its manipulation is easy. 



SPECIAL TREATISE OX DOUBLE STAES. 



A work is now preparing in England which will be of im- 

 portance to all observers of double stars, and to those inter- 

 ested in the calculation of the orbits of binary stars. Its 

 joint authors are Mr. Gledhill, Mr. Crossley, and Mr. Wilson 

 of England, all expert double-star observers, and Dr. Do- 

 berck, of Markree, Ireland, to whom we owe the investigation 

 of many orbits of binary stars. 



Mr. Gledhill is to write on the observations of double stars, 

 binary star-orbits, and the history of the subject; Mr. Cross- 

 ley describes the various micrometers and their use, etc. ; 

 Mr. Wilson gives an account of the various graphical meth- 

 ods of calculating orbits of binaries ; and Dr. Doberck treats 

 of the analytical investigation of such orbits, with examples 

 chosen from his researches on Sigma and Gamma Coroiice. 



THE CORONAL-LINE 1474 K. 



The line 1474 of Kirchoff's scale, which is reversed in the 

 spectrum of the solar corona, is known to nearly coincide 

 with one of the short lines in the iron spectrum when the 

 Leyden-jar spark is used (not with the electric arc between 

 carbon points). Even with powerful spectroscopes it appears 

 in the solar spectrum as a fine, hard, black line. Professor 

 Young, of Dartmouth College (the discoverer of the line in 

 the solar corona), has examined and mapped the neighbor- 

 hood of this line in the diftraction spectrum produced by re- 

 flection from gratings ruled by Mr. L. M. Rutherfurd ; and 

 he finds this line to be unmistakably double. The two 

 components are separated by a distance of about j- of a 

 division of Angstrom's scale, i. e. about ^^r o^ ^^^^ distance of 

 the D lines. Tlie more refrangible component (which Young 

 considers to be the coronal-line) is heavier and more hazy 

 than the other, which is well defined. Three gratings (6480, 

 8640, and 17,280 to the inch respectively) have been used, 



