1823.] ^^of. Camming on the Galvanoscope, 289 



Fig. 1, the galvanoscope. 



A K, tubes tilled with mercury, to be connected with the gal- 

 vanic plates. 



ABCDEFGHK, a wire placed in a spiral form, round the 

 compass needle n s. 



a b Cf d efy brass wires inserted in the galvanoscope, and car- 

 rying the sliding wires b g and eh. 



i k, I m, the neutralizing magnets attached to the wires b g 

 and e h. 



op q r, a brass wire inserted in the galvanoscope at o, and 

 carrying a small magnet moveable round q r. 



The galvanoscope is placed east and west; th6 compass 

 needle is then brought nearly into the plane of the spiral by the 

 large magnets i k, I m, and the adjustment is completed by the 

 small magnet t v. 



It is desirable that the spiral wire should not be less than 

 ]-25th of an inch, and that there should be as little space as 

 possible between the spiral parallelogram and the compass 

 needle. 



There should be at least four or five revolutions in the spiral, 

 of which the vertical form, fig. 2, seems preferable to the hori- 

 zontal, fig. 3, as permitting a better view of the needle. 



Article XI. 



Remarks on M, Lo?2gchamp*s Memoir on the Uncertainti/ of 

 Chemical Analysis. By Richard PhiUips, FRS. L. and E. &c. 



In this paper* M. Longchamp has detailed a great number of 

 experiments performed with the intention of ascertaining the 

 cause of the uncertain results which he obtained in analysing 

 sulphuric acid and sulphates, by means of barytic salts. The 

 subject is one of unquestionable importance, and if the experi- 

 ments detailed by M. Longchamp are accurate, his inferences 

 are just, and chemical analysis is at an end. As, however, all 

 statements which tend to envelope the sciences in uncertainty 

 are productive of mischief, by discouraging their cultivation, I 

 shall endeavour to show that the evils to be apprehended from 

 M. Longchamp's experiments are merely imaginary ; and without 

 minutely examining all the details into which M. Longchamp 

 has entered, I think it will appear from his statements respect- 

 ing the action of the barytic salts upon sulphuric acid, that but 

 little confidence can be placed in his results. 



One hundred parts of sulphuric acid of specific gravity 1*812 



• Annales de Chimie et de Physique, torn, xitiii. p. 1 55. 



New Series J vol. vt. u 



