370 A Method of correcting the Variation of 



pearcd. Some may say, that in the present instance the 

 deranged state of the skin and of the bowels was the 

 eflect of the disease, and that the treatment adopted re- 

 moved the effect without first removing the cause: but 

 this case (as well as many others) clearly proves to me the 

 importance and great necessity of paying strict attention to 

 the slate of the skin, and of the alimentary canal, in every 

 disease. 



I am, with all due respect. 



Your humble servant, 



Hatton Garden, May 16, 18i2. JOHN BuRNE. 



LIV. A Method of correcting the Variation of the Mariner's 

 Compass. By Mr. John Hodgson, Charles Street, 

 St. James's Square*. 



Sir, X TAKE the liberty of requesting you to submit to 

 the Society for the Encouragement of Arts, Manufactures 

 and Commerce, a small theodolite, to which an addition 

 has been made, calculated, it is hoped, to be of some utility. 



The frequent recurrence to the variation of the compass, 

 which is necessary in the use of the theodolite, is always 

 attended with trouble, and not unfrequently productive of 

 error. 



It appears to me, that by a very simple expedient these 

 inconveniences may in a great measure be removed. To 

 the magnetic needle of the instrument, let one of brass be 

 affixed moveable upon the centre of the former ; the brass 

 needle may be termed the corrector. Nothing more is ne- 

 cessary than to place the magnetic needle and the corrector, 

 at the angle of the variation, in such a manner that, the 

 former being in the magnetic meridian, the latter shall be 

 in the irue meridian. The south end of the corrector will 

 point to the true bearing of an object seen through the 

 sights of the theodolite. 



J also beg to lay before the committee a ship's compass, 

 in which will be found a different application of the same 

 principle. In this instrument, the needle is made move- 

 able under the compass card, so as to be placed by the 

 officer of the watch, or any other proper person, under the 

 variation line, as often as an aziiiiuth or an amplitude shall 

 have been taken. The points of the compass will, by these 



* Vrom Tranxaclinns of the Society for Ihe Encojiragetnetit of Arts, Manu- 

 factures, and Commerce, ior 1811. The silver medal of the Society was 



voted to Mr. Hodgson for this comtnunicatioB. 



means, 



