252 
DR. J. YOUNG AND PROFESSOR G. FORBES ON THE 
Translation of the chronograph records. 
The most usual way of observing with the chronograph was to complete the electric 
circuits for the clock and the rotating mechanism during the hour or two that we 
might be at work. The circuit which when closed brings the pens into contact with 
the smoked cylinder -was however kept open, the means of closing it being a contact 
key in the hand of the observer. The assistant winds up the chronograph (which can 
only go for about 20 seconds) and levels it. He also examines the pens to see that 
they are in working order. The observer winds up the mechanism. He notices that 
his contact maker is in good working order. He oils the pivot holes of the mechanism. 
He puts on the number of weights which experience tells him will give the required 
speed approximately. He asks “ Are you ready ? ” When the assistant is ready the 
observer releases the brake on the mechanism. He may if he please count the number 
of eclipses of A or B before his final speed is obtained. He adjusts the width of the 
teeth by raising or lowering the mechanism by means of one of the levelling screws. 
When the speed which gives equality of lights is nearly obtained he notices and 
records whether A or B is increasing with increase of speed. He makes the equality 
of lights more exact by adding to or taking from the driving weights, or by pulling 
the catgut supporting the weights either up or down, or by touching the milled head 
on the arbor of the second wheel on the mechanism, or in such a way as he has 
decided upon, until he feels that he has complete power to produce equality of lights. 
He then says to the assistant “ Begin.” The assistant gives a definite speed (judged 
by the eye) to the fly-wheel and cylinder of about one revolution a second. After a 
few seconds the observer assumes that the cylinder is rotating uniformly. He makes 
contact. The pens touch the smoked cylinder. The assistant immediately begins 
to lower the support of the pens by means of the rack and pinion, so as to make the 
pens describe spirals close to each other, the pens meanwhile marking seconds of the 
clock, and hundreds of revolutions of the toothed wheel respectively. The observer 
now adjusts the speed so as to produce equality of brightness in the tw r o stars. When 
he is quite certain that he has attained this he breaks contact for one-eighth of a second 
or thereabouts. This leaves a blank in the spiral traces, the commencement of which 
indicates the time at which the speed is required. 
The 12th and 13th equalities were generally used, and sometimes the 14tli. 
Successive observations were always made at successive equalities to allow of the 
complete elimination of errors alluded to in the theory of our method. 
The cylinder is completely covered after four or five observations have been made. 
After the spirals have been traced by the clock-pen and the wheel-pen upon the 
smoked cylinder of the chronograph, the divided circle and vernier are attached to 
the instrument, the former being divided into 500 divisions, and the latter reading to 
Tooooth of a revolution. The microscope with its cross wires is placed so that the 
irregularities marked by the pens on the spiral traces can be readily seen, and brought 
