474 C. C. Hutchins — Notes on Metallic Spectra. 



Art. XLIX. — Notes on Metallic Spectra', by C. C. 

 Hutchins. 



In the work herein described an attempt has been made to 

 determine the wave-length of several metallic lines with some- 

 thing of the precision with which wave-lengths of solar lines 

 are known and tabulated. 



It has been repeatedly pointed out that wave-lengths of 

 metallic lines from the determinations of the best observers are 

 liable to errors of one part in 3000 or 4000 ; while Rowland 

 has given us the position of a long list of solar lines correct to 

 one part in 500,000. It is too often forgotten that Thalen 

 used a single bisulphide of carbon prism in his researches, and 

 that consequently, his places can in no sense be considered 

 standards of precision for the more powerful instruments of 

 the present time, 



The spectroscope employed in the present work has a large 

 flat grating with ruled space o cm by 8 0m . Upon the margin of 

 this grating Professor Rowland has written : " Definitions 

 exquisite." The collimator and view telescope are combined 

 in a single lens, an excellent objective by "Wray, six inches in 

 diameter, eight and a half feet focus. The radius of curvature 

 of the back surface of this lens equals its focal length, so 

 that the ray reflected from this surface passes back to the slit, 

 and any objectionable illumination of the field is avoided. 

 All parts of the instrument are so contrived that it is operated 

 without the necessity of the observer leaving his seat at the 

 eyepiece. A heliostat and achromatic lens of five feet focus 

 form an image of the sun upon the slit. Thus arranged the 

 instrument easily performs all tests of spectroscopic excellence 

 with which the writer is familiar. To produce the metallic 

 spectra an eight inch spark condensed by a number of jars 

 having about 6 sq. feet of coated surface, has been employed. 

 The spark is produced immediately before the slit, the jaws of 

 which open equally. The coil is operated sometimes by a 

 dynamo, and sometimes by the current from a storage battery. 

 A review of all the spark spectrum lines has been made with 

 the arc, and a few lines added to those that the spark gave. 

 A steam jet* was employed to increase the luminosity of the 

 spark. The work has been confined to the lower portion of 

 the spectrum, where it still appears that eye observations have 

 advantages of the photographs. 



The position of a metallic line is determined by bringing 

 the crosswire of the micrometer upon it, letting in the sun- 

 light, and moving the crosswire to one of the standard lines 



* This Journal, Feb., 1889. 



