﻿Dr. W. Huggins on a Registering Spectroscope, 545 



last, led me to seek some method by which the positions of lines ob- 

 served 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 illumi- 

 nated scale. 



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

 this object could be satisfactorily accomplished by fixing in the eye- 

 piece 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 

 conditions, and also with a similar instrument with some modifi- 

 cations 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 pro- 

 bable that similar instruments 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 telescope, 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 spec- 

 trum from the red to the violet. Under the extremity 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 coincidence 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 de- 

 note that the line recorded is a bright one. 



It was found that from ten to twelve Fraunhofer lines could be 

 registered in about 15 seconds, and that, when the same lines were 

 recorded five times in succession on the same card, no sensible 

 difference of position could be detected between the pricks register- 

 ing the same line in the several spectra. 



