166 H. M. Parkhurst on a Star-Mapper. 
As an illustration of the ease with which the apparatus may 
be adjusted with sufficient accuracy for the identification of the 
stars, I will state that I have found it easy to take a succession 
of twelve 15-minute maps, in selected places varying many de- 
grees in right-ascension and declination, in but little over three 
ours. 
The minor details, such as the mode of supporting the vari- 
ous centers of motion, the mode of securing the requisite ease 
and accuracy of motion at the various centers without lateral 
motion, the mode of securing the proper motion of the paper, 
the mode of making the universal joints, &c., may be varied ac- 
cording to the — accuracy and the allowable expensive- 
ness of - oe appar. 
Some of ae poner it may be well, however, to refer to 
more Fi 
he perpendicular arm of the right-angled lever A is of board 
about nine inches wide, connected at the left end with the star- 
ock-pendulum i is a by the stout bar which supports 
the center C, 
It is important that lateral motion should also be guarded 
against at the center C, and at the center of motion of the star- _ 
point-bar, shown in figure L Bech of these centers is there-_ 
fore constructed with pivots sufficiently separated to accomplish 
that object. The ends of the rod E are connected with slides 
clamped upon the respective ee B and D, so as to be easily 
varied in adjusting the rate of motion of the star-point. The 
simplest mode of making a universal joint, and that which 
I have therefore adopted in my own mapper, is bending the 
ends of two wires snugly around each other. 
The arm of the star-key K moves horizonta Hy, and i 
pivoted opposite the center of the paper, to the left, eecribing | 
an arc exactly equal to that described by the star-point, but 
of about three times the radius. It strikes an adjustible stop 
on each side by which the width of the map is limited. Th 
star ea itself I have used in many different forms. The only 
form as been satisfactory, although not constructed 
with — "ati Sige as I should sarpeea is the fo! owing : 
e star-key is compound, co nsisting of a series of eight 
vertical keys or manuals, onlee. of which may be used at — 
