] 80 SCIENTIFIC NEW*. 



Ma ,'ne' ;cal 

 teleicope. 



versing, because this last operation- is, in most cases, imprac- 

 ticable. Mr. Troiighton's magnetic telescope may be turned 

 round in its support like that of the levelling instrument ; and 

 it will determine the magnetic meridian, whenever any one and 

 the same distant object is seen, upon the centre of the cross 

 wires alter the telescope has been turned half round on its axis, as 

 in its former state. By this contrivance the diurnal and the 

 .other variations, to which the magnetic bar is subjcet, may be 

 easily observed, and it may even be ascertained whether the 

 direction of the magnetic force varies with regard to the axi& 

 .of the tube.. As the present notice is intended to be short, and 

 as I hope for farther communication from the inventor, I for.^ 

 bear to enter upon observations respecting the kind of instru- 

 ment to which this telescope may be attached. It is evident 

 that observations for the dip and variation may easily be made 

 by reference to tlie plumb line, and to the heavenly bodies. 



Mr. Troughton is already engaged in the executing orders 

 received for this instrument, as well from scientific men of this 

 kingdom, as from those on the Continent., The learned reader 

 will recollect several instances, in which the eye-peice of a 

 telescope, applied to its focal image, has, with great conveni- 

 ence and precision, aftbrded angular determinations which 

 could not with the same convenience have been observed in the 

 tisual methods. The application of a magnifier to the extre- 

 mity of a magnetic needle is also attended with difficulties, 

 which Mr. Troughton's invention will dbviate; at the same 

 time that it facilitates and extends our views of a very curious 

 ' and useful natural power. Among those active philosophers 

 .who do not wait for the construction of instruments, or cannot 

 atford to make purchases for all their several OGcasit.ns, this 

 contrivance will suggest experiments,- which may be made by 

 tyeing together a telescope and a magnetic bar, and suspending 

 them by a thread or fine wire, for some of the purposes of obseE- 

 vation which they may be disposed to make. This, though 

 a clumsy instrument, will also bear reversing, and may be 

 usefully applied. 



New 



