[ 129 ] 



the Royal Irifli y^cademy. For permanent f-ations, which may 

 hs feen clearly with tolerable glalfes at twenty miles diftance, 

 ftone or wooden pillars fixteen or twenty feet high mud be 

 folidly credled ; on the top of thefe a moveable circle or plat- 

 form turns horizontally upon a centre : — on this platform an 

 axis ruoves vertically and c.irries the arm or pointer along with 

 it. Fight handles turn the pointers, which are fixed in their 

 differe-.t pofitions by a catch or alidad. By means of the plat- 

 form the pointer may be turned to any part of the compafs, 

 and as one fide of it is painted black and the other white, either 

 fide may be employed, ab the colour of the clouds or the fitua- 

 tion of the place may require. 



Besides thefe permanent machines, of which dimenfions and 

 a defcription are fubjoined, Plate I. I make ufe of portable 

 machines, fwhich may be detached like Tentacula from the main 

 body in hazy weather) confifling of pointers ten or twelve feet 

 high, and of a light triangular ftand, which can be eafily 

 faftened with tent pegs to the ground : Thefe may be lodged in 

 any houfe near the place where they are ufed, or in times of 

 danger may be carried back to the permanent ftations every 

 night. 



In managing a correfpondence by thefe machines, it is ne- 

 ceflTary to have certain fignals eftabliflied ; nor are thefe fignals 

 merely arbitrary ; it is abfolutely neceffary that they fhould be 



Vol. VI. R made 



