J02 An Account of the Repeating Circle, 



" I am happy to have it in my power to give you a most 

 favourable account of the oxymiu'iate of potassa. 



*' I have given it in several cases of both active and passive 

 haemorrhage with the best effects, as well as in the synochus. 

 It seems to have the very speedy effect of lowering the pulse, 

 and as much so as the digitalis, but with this difference : — so 

 far fi'om reducing the strength of the system, it, on the con- 

 trary, improves it. I have also given it in two cases of indi- 

 gestion, arising from a torpid action of the liver, with decided 

 advantage. I intend to persevere in the use of it." 

 I have the honour to be, 

 Gentlemen, 

 Your obliged and very obedient humble servant, 



J. Murray. 



XX. An Account of the Repeating Circle, and of the Altitude 

 and Azimuth Listrument; desa-ibing their different Construc- 

 tions, the Manner of performing their principal Adjustments, 

 and hoxo to make Ohservcdions with them ,- together xvith a 

 Comparison of their respective Advantages. By Edward 

 Troughton, Esq. F.R.S. and Member of the American 

 Philosophical Society/. 



[Concluded from p. 18.] 



Manner of using the Altitude a7id Azimuth Ciixle. 



In geodesy this instrument, being adjusted, measures without 

 further trouble angles between objects upon the horizontal 

 plane, whatever may be the number required to be taken at 

 one station. The parts of the instrument are all concentric, 

 and therefore whatever it gives, whether the objects are re- 

 mote or near, requires no correction. The angles having been 

 read off individually will be vitiated by the errors of division; 

 and even in graduation that may be deemed good, those errors 

 may be too great in some cases that occur. Such cases are 

 well known to the judicious surveyor, and may be obviated by 

 simply turning the whole instrument upon the stand, and setting 

 the axis vertical ; again and again taking the angles which he 

 wishes to ascertain with the utmost accuracy: for, by this ex- 

 pedient, he will get any angle upon as many different paits 

 of the circle as he pleases or thinks necessary. This may at 

 first view appear to be a principle derived from the other in- 

 strument; but let it be remembered that it is no more than 

 taking means ; a thing practised and well understood before 

 the repeating instruments were brought into existence. 



In 



