HI, M. Parkhurst on a Star-Mapper. 163 
that of the spark itself. In all probability this is also the case 
in a jar charged by frictional electricity, and may serve to ex- 
plain the great discordance between the results obtained by 
Wheatstone and Feddersen, the method used by the former 
furnishing only a view of the first act, the eye being too much 
dazzled to perceive those that are subsequent and of far less 
intensity. 
Art, XVI.—The Star-Mapper ; by Henry M. Parxuurst. 
Harty in the year 1856, I commenced the construction of a 
star-mapper, designed to extend the principle of the Chrono- 
graph, which maps right ascension only, to an instrument 
mapping both right ascension and declination. On the 7th of 
October, 1856, having completed with my own hands the 
necessary apparatus, I took my first map. 
in my first apparatus a concave lens was moved in declin- 
ation, perpendicular to the axis of the eye-piece, the telescope 
being fixed in the meridian and the stars as they crossed the 
field of view were thus optically brought in succession to the 
crossing of two fixed illuminated wires, A few levers conver- 
ted this motion into a horizontal motion of the marking point 
or star-key, at right angles with the motion of a roll of tele- 
graph paper one inch wide carried by a clock movement. Strik- 
ing the star-key, at the instant of the transit at the center of 
the field, mapped the star in its proper position. In order to 
ke a map several degrees in width, I omitted the concave 
lens and moved the telescope itself in declination, with a 
slightly varied system of levers. 7 
So far there was no difficulty. But a star-mapper which 
would only map in the meridian would have been to me value- 
less ; and I reconstructed and rearranged very mapy times the 
system of levers by which I could convert the visible motion at 
any desired allactic angle into a horizontal motion of the 
Star-key. My experience in the fall of 1856 convinced me t 
my apparatus had two radical defects. _ ons 
1. The motion of the telescope to obtain the declination was 
troublesome, even for a 3-foot telescope, owing to the neces- 
accuracy as to make this method of mapping possible. And 
further, when the telescope is clamped we have twice the ini- 
