TRANSACTIONS OF SECTION A. 899 
“to it. The author pointed out that this mode of procedure leads to two equations 
~which suffice for the determination of the horizontal component of the earth’s 
~magnetic field, and also of the effective length of the deflector. In these equations 
the also showed that the leneth of the deflector entered as a minus term in the one 
‘and plus in the other, and thus rendered the observations highly sensitive to pos- 
sible errors in that term, and enabled a good estimate of the effective leneth of the 
different deflectors to be had. Apparatus was described by which the whole cycle 
of observations, both for this and the oscillation experiment, might be obtained 
“without the necessity of handling the deflector magnets. 
The effects of the various corrections on the value of ‘ H1’ derived from the 
-equations were discussed. Such of the errors as were sensible had been made the 
“subject of direct experiment, and their effect allowed for in the table of values of 
‘ H’ given in the paper and quoted below. 
As the observations necessary for a determination of ‘H’ by this method 
-extend over such a time as may make the diurnal variation sensible, and further to 
-guard against the readings being vitiated by undetected magnetic storms, a mag- 
netic vibrator was kept going throughout the time of the experiment, and its period 
-taken from time to time as might be found necessary. 
, lse |¢33 | 22 SE 
»|S le | 8 [s88 |88S | SFi 8 ‘| 88]. 
sie |= |& (SPP |222 | 22) 44] 84] a, |e 
a\A |= | Se |sets|ee8a| oS | 58) 3S) sa |= 
Als-|@.| 82 |=So5/.8,8| 83/22/82 | #2 33 
185 || 22/282) 48 e8s|B5ee| 28) P2/ 82] sa | Sz 
Soe) Sale, colee_s pas) eS | FS | ae 
o)—"le |e" lasfelesee | se| Se | 22) 8° | 2% 
BIS | | 2 lg8"a/3e"3/ 83) S8/ee) 84 ls 
Ss] se c oO San lame. =o ort 2A 
al = 2 a eBSs(S2e5)/ aa] & go = 
ag alt Ei 228e(sF9s)/uP/F | ws 
BAtela~zlezelas “Ss 
May 27| 1/0-21 | 8-03 | 3-050 | 32:06 | 28:75 |108-7| 6-91 /44-9 |-1521 
» 27| 2/0:21 | 8:05 | 3-063 | 32:06 | 2875 |108-7) 7:10 58:5 |-1524| 1.55 
» 28] 3/0-21 | 8:05 |3-075 | 32:06 | 28-75 |108:7| 6°31 |54-1 |-1521 
» 29| 4/0:21 | 8:05 | 3-067 | 32:06 | 28-75 |108-7| 7:11|52°3 |-1522 
June 5| 5/021 | 4:00 | 1:526 | 30:0 | 25-125)108-7| 3-12/35-2 |-1524 
» 5| 6/021 | 3-99 | 1-522] 30:0 | 25-125 | 108-7] 3°727/33-7 |-1524 | |-1525 
» 5) 7/0-21 | 4:00 [1525 | 30:0 | 25-125 |108-7| 2°33 /31-7 [+1527 
» 10| 8/0-21 |14-933| 5-646 | 51-9 | 38-85 | 108-7| 13-22 |55°8 (1527) 
» 11] 9/0-21 /15-030| 5-727 | 51-9 | 38:85 |108-7| 12-82 64-3. |-1525 | |-1526 
»» 11/10] 0-21 [15-021] 5-666 | 51-9 | 38-85 |108-7|13-58 [54:5 1527) 
Aug.21|10/ 0-20 |10-01 | 2318 | 35:0 | 30:0 [128-9] 9:14/71-0) |,.5¢ 
| ,, 21|12/020 oor |2336| 35-0 | 300 |128-9) 914 62-7} 2° 
»» 26/11/0-20 |10-01 | 2318 | 35:0 | 30-0 [128-9] 8:91 71-0) | 1557 | lyse 
» 26|12/0:20 |10-01 | 2:336 | 35:0 | 30-0 |128-9] 8-98 \62-7)|~°* 
» 31/13/020 10-00 | 2318 | 35:0 | 30-0 |128-9) 914'70-0}| 159 
» 31/14/0-20 |10-005| 2:336 | 35:0 | 30:0 [128-9] 9-14 61:8!|°° 
6. On Atmospheric Electricity? 
By Professor C. Micuiz Suira, B.Sc., F.R.S.E. 
The commonly accepted opinion, that during fine weather the air potential is 
salways positive, is not accurate for Madras. There it is found that with a dry 
dJand wind (‘.e.,a westerly wind) the potential of the air is usually negative during 
__-Several hours of the day. In the early morning, and up to about 9 a.., the 
eal is usually positive, then it becomes negative, reaching a maximum 
‘between 10 and 11 a.at., and continues negative till the sea breeze sets in in the 
1 Corrected to noon for diurnal variation, 
? Published in full in Phil. Mag. Nov. 1885. 
5 
3m 2 
