106 Prof. Struve on the large Refracting Telescope 



about 2000 pounds. The whole is constructed so as to be 

 used as an equatorial. 



The lower part of the frame of the instrument is formed 

 by two cross beams 9 feet 8 inches long, 7 inches wide, and 7\ 

 inches high, which are strengthened by four smaller bars, form- 

 ing a square. (See Plate VII. No. IV. of this Journal.) They 

 are fastened down by eight screws, penetrating them perpendi- 

 cularly, four at the extremities, and four more towards the 

 centre, and by these screws the instrument is firmly secured. 

 In the centre of this support is fixed an upright post, 6 feet 

 1 inch high, and 7 inches square. Three posts of an elliptical 

 form support this upright to the north east and west : a beam 

 of equal length inclining towards the horizon under an angle 

 equal to the height of the pole rests on the sloping top of the 

 uprio-ht post, and on that part of the lower frame-work which 

 faces the south. This is all the wood about the frame-work, 

 the whole of which is made of oak, and elegantly inlaid with 

 mahogany. The posts are connected by means of 29 screws, 

 which keep it free from every vibration or shaking. 



The upper part of the instrument consists of the tube, with 

 its axis of motion, two graduated circles, and a variety of le- 

 vers and counterweights, producing the most perfect equili- 

 brium in every direction, and preventing any sort of friction. 

 The posts of the principal axis are fastened to the beam of 

 the pedestal, which inclines towards the pole of the earth by 

 means of eight screws passing through the whole thickness 

 of the wood. This axis (parallel to the axis of the wood) is 

 made of steel, 39 inches long, and of proportionate strength. 

 It turns in two cylindrical collars, and lies with its lower end, 

 which is convex and highly polished, on a steel plane, so that 

 it is only in contact in one point. On this axis, towards the 

 lower part, is fixed the hour circle of 13 inches, on which half 

 a second of time may be easily read off. 



The brass box or frame of the second axis is fastened to 

 the upper part of the axis by means of twelve strong steel 

 screws. Through this passes the second axis at right angles 

 to the first, with which it is almost equal in dimensions. It 

 therefore always lies parallel to the equator. At one end of 

 it is the declination circle of nineteen inches, divided into 



