228 Translation from the AstrojiomicalJour. of Hamburgh. 



at their ends the screw work for the stands by which the in- 

 strument rests upon three vertical cones of brass, fastened 

 to the wooden stand of the instrument ; between this and 

 the six horizontal conical arms there is room for the verifi- 

 cation telescope, which has precisely the arrangement of a 

 transit, and hangs in its Ys, which are fastened underneath 

 to two opposite radii. This telescope has no lateral motion, 

 but the wires in the focus are directed by means of a screw, 

 to the object which is taken as the point of comparison du- 

 ring an observation. In the same hexagonal centre piece is 

 fastened the vertical axis, eleven inches long, and two inch- 

 es in diameter. Upon this revolves a drum nine inches in 

 diameter, and five and a half inches high ; upon the upper 

 surface of this, stand two columns bearing the Ys for the 

 transit telescope by which the observations are made; this is 

 a complete transit, and the columns are sufficiently elevated 

 to allow its passage through the zenith. The horizontal an- 

 gles are measured by the revolution of this upper part of the 

 instrument, upon the vertical axis, and are read off" by three 

 micioscopes, which are fixed at the end of as many conical 

 arms, coming from the central drum, each having a micro- 

 meter screw. The illumination is made through the axis of 

 the telescope, the one side of which is perforated, the other 

 has an altitude circle of six inches diameter. The axis is 

 about twelve inches long, which is more than the interval 

 between the columns. Its supports are therefore set upon 

 pieces of brass, elevated above the columns, and extending 

 outwards ; they have the same kind of vertical adjustment as 

 the large transit described above. 



In relation to the observations with this instrument, Mr. H. 

 properly remarks : that the eccentricity is equally corrected 

 by means of tluee equidistant readings, as by two, four, or 

 so on; he also shews, that when the vertical axis is not per- 

 pendicular to the plane of the horizontal circle the errors 

 of the angle will be corrected if the position of the instru- 

 ment's place is alternately changed to the three truncated 

 cones of the stand, so as to give the three regularly succeed- 

 ing positions of a full revolution. These three observations, 

 eacli made in the two diametrically opposite positions of the 

 telescope, and by a half revolution of the instrument, give 

 a mean which is free from eccentricity, from any error arising 

 from the inclination of the circle towards the axis, or from any 

 inequality in the supports of the axis, the readings being be- 



