46 Mr. Fiaunhofer on the Construction 



ing a ring towards the hour-axis. This ring touches(by means 

 of two other axes placed opposite one another) a second and 

 smaller ring ; and this ring turns on the case containing the 

 axis of declination ; so that also with respect to the hour- 

 axis the telescope is exactly balanced in every direction. In 

 order to prevent the friction of the houi-axis and its pressing 

 on its bed, another weight is added, operating on the bed of 

 two friction-rollers. By all these dispositions the telescope, 

 notwithstanding its immense size, may be moved with one 

 fingei% 



The pedestal is of such a shape, that, although its position 

 must never be altered, it cannot hinder the telescope from 

 being turned towards any point of the heavens. It seems, in- 

 deed, that there may be situations of the telescope, in which 

 the -])edestal may be an obstacle against following the star; 

 yet the instrument is so constructed that the telescope may be 

 directed in two ways upon one and the same object, simply 

 by turning the hour-axis 180'^. Thus, if the pedestal should 

 be an obstacle on one side, the turning of this axis will render 

 the telescope free on the other. 



As it is very difficult with a large telescope to find an ob- 

 ject and bring it within the focus, it is usual to add to it a small 

 one, the axis of which is perfectly parallel with that of the 

 lar<je one. The finder of the laroe refractor has 29 lines 

 aperture, and 30 mches focus. 



Each of the two principal axes has a graduated circle, called 

 the hour and declination circles. These are fastened to their 

 axis and turn with them. The division of the hour-circle 

 shows 1- seconds of time, and that of the declination-circle 

 10 seconds of space. By this means those stars which are 

 out of the meridian may also be found and observed in the 

 daytime, which is particularly useful with fixed stars of the 

 1st magnitude, which cannot be observed so well in many 

 particulars at night. 



There are yet many other parts about this instrument, the 

 use of which can however be illustrated only by a detailed 

 description. t-' 



* I'RAUNHOFER. 



Postscrijyt. — The above description was not originally des- 

 tined for the press, nor was it written for astronomers ; it 

 therefore contains much that is superfluous. A detailed de- 

 scription ought to be accompanied with designs of the several 

 parts. I had only drawn the whole of the instrument in a 

 perspective view, from the side on which the clock-work is 

 • . fixed. 



