1871.] Dr. W. Huggins on a Registering Spectroscope. 317 



II. " On a Registering Spectroscope." By William Huggins, 

 LL.D., D.C.L., F.R.S. Received January 14, 1870. 



The short duration of the totality of the solar eclipse of December last, 

 led me to seek some method by which the positions of lines observed in the 

 spectrum of the corona might be instantly registered without removing the 

 eye from the instrument, so as to avoid the loss of time and fatigue to the 

 eye of reading a micrometer-head, or the distraction of the attention and 

 other inconveniences of an illuminated scale. 



After consultation with the optician Mr. Grubb, it seemed that this 

 object could be satisfactorily accomplished by fixing in the eyepiece of the 

 spectroscope a pointer which could be moved along the spectrum by a 

 quick-motion screw, together with some arrangement by which the 

 position of this pointer, when brought into coincidence with a line, could 

 be instantly registered. 



I was furnished by Mr. Grubb with an instrument fulfilling these con- 

 ditions, and also with a similar instrument with some modifications by 

 Mr. Ladd, in time for the observation of the eclipse. 



Unfortunately at my station at Oran, heavy clouds at the time of totality 

 prevented their use on the corona ; but they were found so convenient for 

 the rapid registration of spectra, that it appears probable that similar in- 

 struments may be of service for other spectrum-observations. 



In these instruments the small telescope of the spectroscope is fixed, 

 and at its focus is a pointer which can be brought rapidly upon any part 

 of the spectrum by a screw-head outside the telescope. The spectrum and 

 pointer are viewed by a positive eyepiece which slides in front of the tele- 

 scope, so that the part of the spectrum under observation can always be 

 brought to the middle of the field of view. The arm carrying the pointer 

 is connected by a lever with a second arm, to the end of which are attached 

 two needles, so that these move over about two inches when the pointer is 

 made to traverse the spectrum from the red to the violet. Under the ex- 

 tremity of the arm fitted with the needles is a frame containing a card, 

 firmly held in it by two pins which pierce the card. This frame containing 

 the card can be moved forward so as to bring in succession five different 

 portions of the card under the points of the needles ; on each of these 

 portions of the card a spectrum can be registered. 



The mode of using the instrument is obvious. By means of the screw- 

 head at the side of the telescope, the pointer can be brought into coin- 

 cidence with a line ; a finger of the other hand is then pressed upon one of 

 the needles at the end of the arm which traverses the card, and the position 

 of the line is instantly recorded by a minute prick on the card. A bright 

 line is distinguished from a dark line by pressing the finger on both needles, 

 by which a second prick is made, immediately below the other. In all 

 cases the position of the line is registered by the same needle, the second 

 needle being used to denote that the line recorded is a bright one. 



