226 Scientifie Proceedings, Royal Dublin Society. 



is no occasion for any second anti-friction ring or bracelet, but a double set of 

 ball bearings is mounted, h b, outside this smaller bearing to take the end- 

 thrust and relieve any friction that might be due to this. 



The one bracelet, B B, shown in section in fig. 2, Plate XIX., which con- 

 tains the live rollers, surrounds the neck of the declination axis near the centre 

 of gravity, and has cast on it two lugs ; one of them, L, the lower, has a hole 

 drifted in it which strings upon a pin attached to the cross-head and fitting it in 

 the direction of x x, but slotted in the direction of y y, so that tlie ring or bracelet 

 is capable of a small amount of motion in the direction y y oi the polar axis. 

 A lever 21, centred on the cross-head at C, applies (as to its shorter end) 

 against the lower side of this lug, while the longer arm of the lever is carried 

 to a convenient distance, and is furnished with a pushing screw P, which 

 bears on a lug attached to the cross-head. When this lever is brought into 

 action by forcing up the screw, a pressure is exerted on the lower side of the 

 bracelet which lifts on the rollers that component of the weight which is 

 represented by the line a c, in diagram fig. 3, Plate XVIII., and which 

 is constant in direction as respects the polar axis. 



On the upper side of the bracelet is another lug with a hole, into which 

 applies the shorter arm of another lever iV iV, centred on a pin C" and working 

 in a plane at right angles to the first described lever. The longer arm of 

 this lever extends beyond the central cube, and has fixed upon it a heavy 

 counterpoise W. 



When the telescope is in the six-hour position, this lever is non-effective, 

 i.e., it is not exerting any force one way or another. All tlie weight carried 

 by the declination axis is then divided between the lever M under the cross- 

 head and the thrust ball-bearings at the end of the declination axis. If, how- 

 ever, the instrument be turned to east or west, the lever N on the top begins 

 to act, and its effect increases in precisely the correct ratio as the telescope 

 is turned, till tlie meridian position is reached, when the thrust on the end- 

 bearing becomes nil (as the axis is horizontal), and all the weight is divided 

 between the lever If below and the lever N above the cross-head. If the 

 telescope be turned to the other side of the pier, the top lever acts in exactly 

 the opposite direction. 



If the weights be properly proportioned and the levers properly set, all 

 the weight of the declination axis and the telescope it carries (with the 

 exception of a few lbs. left on Y bearings to ensure steadiness) can be carried 

 on the rollers of this " bracelet." 



