Hf, M. Parkhurst on a Star-Mapper. (167 
pleasure to impress the paper. These manuals are enclosed in 
a cylindrical box, and the series may be revolved horizontally 
by turning the knob on the top of the box, a projecting pin 
indicating by its direction which of the keys is to the right 
hand. This pin having been turned as desired, pressing on the 
knob, locks the plate holding the series of manuals from 
further horizontal rotary motion, and depresses the manuals 
so that they nearly touch the paper. The outside casing is 
cut away above the manual to the right, so that at the proper 
instant that may be struck by the finger to impress the paper 
in the proper position. 
ot only are the several manuals thus interchangeable, by 
the rotation of the series, but each of the eight manuals may 
be turned upon its own axis, Thus, that with which I indi- 
cate the 10th to the 13th magnitude, impresses upon the paper 
a short dash like a hyphen, pointing in any required direction; 
the horizontal dash indicating the 10th magnitude, and a rey- 
olution of 45° being allowed for each lower magnitude. The 
brighter stars are indicated by more conspicuous forms ; and 
there are special marks for double stars, clusters, nebule, &c. 
‘he approximate form of the impression upon the paper is — 
given to the top of the manual, so that any error in bringing 
the wrong manual to the right, would be instantly detect 
and rectified before impressing the paper. 
_ The star-maps thus impressed, if the paper is of good qual- 
ity, do not need inking ; but I have marked with pencils and 
ink of different colors, such stars as I have recognized upon 
two or more than two maps, in order that any new stars might 
be conspicuous from their remaining unmarked. 
ave used paper cut in strips of the proper width and 
wound upon a roller at the left of the star-key and beneath 
the arm of the star-key. The end is passed between guides 
and over the mapping cushion, between the rollers which are 
carried by the clock movement, and then the paper is wound 
upon another roller, also carried by the clock movement. The 
gradually increasing size of the roller on which the paper is 
wound, from the addition of the paper, is compensated for by 
a spring, which is at first gradually relaxed and afterwards 
again tightened ; but which is sufficiently wound up by a key 
fore commencing to map, to keep the paper always tight. 
In the action of the levers of the mapper, arranged as above 
described, there is a slight theoretical inaccuracy, which, in my 
Own instrument, is sufficiently compensated for by two expe- 
dients, but which may be entirely removed by a slight change 
the construction. For instance, as described, the motion of 
the lower end of the arm A is exactly equal to that of K in 
