5 
: App. | App. : App. | App. ¢ App. 
Tone Te dtesda ler me Th | wet. || «Time | ae 
ny os | age yma 5 ly ms 
1257. «—-0'| 11°65} +03 5 14 30 | 18-45/+0-45 || 9 11 30) 21-0 
15 | 11-65 | +0°3 45 | 184 | +0°5 45 | 20:95 
30 | 11-6 | +03 15° 0 }'184 | 4-0-5 12 0} 21:0 
45 | 116 |+03 15 | 18-4 |+0-45 15 | 21-0 
58 0} 115 |404 | 30 | 18°45) +0-45 30 | 21:0 
D570") 10:7") O35 7 27 PO" 20-7 0-0 OSG! Tears: 
15 | 106 |+0-4 20-7 0°05 15 | 20°7 
30 | 106 | +04 20:8 | —0-1 30 | 20°6 
45 | 10° | +0-45 0 | 20°83 | —O0-1 45 | 29-65 
58 OO} 105 | +0-45 15 | 20°85 | —0-05 19.2,204).20:7 
15 | 105 | +045 30 | 20:9 0-05 15 | 20°65 
30 | 106 |+04 | 45 | 20:9 0-0 30 | 20°6 
45 | 10-7 |+0-35 | 28 = 0.| 20-85) +0:05 45 | 20°55 
59 0 | 10°65) +0-4 15 | 20°9 0-0 18 0} 20°55) + 
4:4 0} 145 |403 9-3 +0 | 21-3 | +0°4 9 23 0 | 20°15)+ 
15 | 144 | +03 15 | 21:3. | +-0°5 15 | 20°25 | + 
30 | 14-4 | +03 30 30 | 20:2 
45 | 144 | 403 45 | 21:3 |+0°4 45 | 20°15 
5 0| 14-45|+0°3 4 0} 21-4 |+0-4 24 0} 201 
15 | 14-45 | +03 15 | 21:3 | 40-4 15 | 20-1 
30 | 14:5 | +0-2 30 | 21:3 | +0-45 30 | 20:1 
45 | 14-4 |40°3 45 | 21-35} +0°55 45 | 20-2 
6 0} 144 |}4025 19 5 O| 21-2 | 404 25 60 | 205 
14 0] 1845)+0-45 ||9 1] 0} 21:0 | +0-4 
) 
15 | 184 | -L0%5 Li 
! 
21-0 | 10-45 
The investigation concerning the use of small magnets now 
appeared complete. We obtain from it two new principles 
respecting the construction of magnetic instruments : 
1. The influence of currents of air produced by changes of 
temperature must be guarded against. by carefully protecting 
the magnets*. 
2. The use of small magnets is not only advantageous, but 
even necessary in exact magnetic determinations, partly because 
they can be more easily protected from the influence of currents 
of air; partly because larger bars, by reason of their considerable 
moment of inertia, cannot show magnetic variations which take 
place in very quick succession. ° 
It might have been desirable to exhibit the influence of cur- 
rents of air on large bars, as has been done above for small 
magnets; it may be easily conceived that under similar cireum- 
stances a current of air will be produced in the box of the large 
magnetometers as well as under the bell-glasses of the small 
* This object would be completely attained by exhausting the air under the 
bell-glass. ‘There would be no particular difficulty in doing this, but I have 
not myself tried the experiment, as I hardly expect from it any important 
practical advantage. 
te 
