438 H. A. Rowland—Absolute Unit of Electrical Resistance. 
If the probable error is subtracted from the first and added to 
the second they will very nearly equal each other. Hence the 
difference is probably accidental. Indeed, by the combination 
of the results it does not seem possible to find any constant 
source of error, and therefore the errors should be eliminated 
by the combination of the results. 
In the final result 
R=34°7192+-°0070 
the probable error, +*0070, includes all errors except the ratio 
of é to G’. Wemay estimate the probable error of G at 
s3,'55 and of G” at +5555. 
Hence the final probable error of R, including all variables, 
iS +5355, Or +°04 per cent, 
or R=34°719+--015. 
The probable error of the British Association determination 
was + ‘08 per cent, not including the probable error of the con- 
stants; and of Kohlrausch’s determination +°33 per cent, in- 
cluding constant errors. 
Comparison with the Ohm. 
The difficulty in obtaining proper standards for comparison 
has been explained above and I shall have to wait until the 
arrival of the new standard before making the exact comparison. 
At present I give the following results, which seem to warrant 
the rejection of Messrs. Elliott Bros’. 10-ohm standard and to 
make that of Messrs. Warden, Muirhead and Clark correct. I 
shall designate the coils by the letter of the firm and by the 
number of ohms. Experiment gave the following results : 
W (10)=1-00171 X E (10), experiment of June 8, 1877. 
Ww (10)=1°00166 xX E (10 i eo ee Ben, 28, 1875. 
W (1,000) : W (100) :: W (10): -999876 E (1), experiment of 
February 23, 1878, ' 
Now the greatest source of error in making coils is in passing 
from the unit to the higher numbers. As the reproduction of 
single units is a very simple process the single ohm is without 
much doubt correct, anid as the above proportion is correct 
within one part in 8,000 of what it should be, it seems to point 
to the great exactness of the standards then used, seeing that 
the exactness of the proportion could hardly have been acci- 
dental. It is also to be noted that Messrs. Warden, Muirhead 
& Clark’s 10-ohm standard agreed more exactly with a set of 
coils by Messrs. Elliott Bros. than their own unit E (10). 
The resistance of my coil as derived from the different stand- 
ards is as follows: 3 
From Elliott Bros. resistance coils.......... 34-979 ohms. 
ue 7, RO AUR BOOS: 35083 “* 
a WM & C's...“ 2 85-0 
“ W., M. & C.’s 100-ohm “ 35°0385 =“ 
ee es sees 
