IN FAVOUR OF MAGNETICAL OBSERVATIONS AT TIFLIS. 313 



The electrical balance used was that described in a paper on the repro- 

 duction of a unit by chemical means in the Report of your Committee for 

 1864. 



With this instrument, two conductors, differing in resistance by not more 

 than 3 per cent., could be directly compared, and the ratio found depended on 

 to 0-0025 per cent. 



Numerous comparisons were made by means of this balance between the 

 following sets of coils, viz. : — 



By taking the mean of several very concordant observations, the value of 

 the coil la was found in terms of the standard, and therefore of the unit, to 

 a great degree of accuracy, and from this coil the first platinum-silver unit 

 was constructed. 



All the coils to be issued are recompared some weeks after they are made, 

 and rejected if they are found to have altered in resistance by 0-01 per cent. 



All the coils sent out are correct at the temperature written on them to 

 within 0-01 per cent., and this temperature lies between 14-5 and 16-5 in all 

 cases. 



Report of the Committee, consisting of Major-General Sabine, P.R.S., 

 Sir John Herschel, Bart., F.R.S., J. P. Gassiot, F.R.S., and Sir 

 It. I. Murchison, Bart., F.R.S., appointed for the purpose of com- 

 municating to the Russian Government the opinion of the British 

 Association, that the establishment of magnetical observations on the 

 Kew system at the Observatory of Tiflis, by Professor Moritz of that 

 place, ivould largely conduce to the furtherance of Magnetical 

 Science. By General Sabine, P.R.S. 



At the Meeting of the British Association at Bath in 1864, a resolution was 

 passed by the General Committee appointing a committee, of which my name 

 stood first on the list of its members, " for the purpose of communicatino- to 

 the Russian Government the opinion of the British Association, that the esta- 

 blishment of magnetical observations on the Kew system at the Observatory 

 of Tiflis, by Professor Moritz of that place, would largely conduce to the 

 furtherance of magnetical science." 



Not having been myself present at the Bath Meeting, and knowing nothing 

 of what had passed there, beyond the words of the resolution transmitted to 

 me by the Assistant-Secretary, Mr. Griffith, I addressed the letter marked 

 No. 1 to Mr. Hopkins, the General Secretary. 



No. 1. 



" 13 Ashley Place, Not. 9, 1804. 

 " My dear Sie, — I received a few days since from Mr. Griffith a notice of 

 a resolution adopted by the General Committee of the British Association at 



