OF THE UNITED STATES. 33p 



according to his own convenience and experience, and also 

 according to the particidar skill or means of the artist who 

 constructs the instrument. The hij!;li opinion whicli I had 

 reason to entertain of so distinguished an artist as Mr. 

 Troughton induced me to leave much to his judgment and 

 ideas. 



I had the horizontal circle constructed so as to have the 

 axes of l)otIi motions. The centre part had cones both 

 downwards and upwards. The axis downwards revolved 

 in the centre of the stand part. The legs of this were in- 

 clined from the centre to the circumference where the per- 

 pendicular screws come and upon which the instrument 

 stands. The other axis receives the upper part of the in- 

 strument by means of a socket similar to that in the other 

 instrument, but much shorter. 



I'hese two axes weie of bell metal, with steel rings at their 

 inner and outer ends. They were differently proportioned 

 to eacli other. The lower was about twice as long as the 

 upper, and of a more acute conical shape, in order to give it 

 a greater wedging power ; which, with the greater superin- 

 cuml)ent w^eight on it, when the circle is moved with tlie up- 

 per part, increased its friction. The upper axis was about 

 two inches long ; its lower diameter was about the same 

 length, its upper less than one inch. The socket of the axis 

 lay close to it, and moved with ease, as the weight of the 

 upper part was light. Accordingly, in moving this part, the 

 great weight of the horizontal circle, and its great friction 

 prevented all dragging of it after this motion. This, in the 

 instruments made by Mr. Troughton, and in wliich the ho- 

 rizontal circle is light, is prevented by completely detaching 

 the circle from the upper part, when the clajnp A is loose. 



Mr. Troughton's objection to this shape of the axes was, 

 that they could not be rubbed so well witii emery in a kind 

 of screwing motion which takes off all the rings of turning 

 and renders them smooth. But as these rings always form 

 themselves in the instrument by use, I should think that in 



