234 Mr. Christie on magnetic 
length of No. 18 ; and the copper needle by the same length 
of this wire doubled. In vibrating these needles they were 
released 90° from zero ; and in order to be certain that the 
extent of the first vibration was the same when the needle 
vibrated in the sun as when it vibrated in the shade, I noted 
also the extent of the arc of vibration on the other side of 
zero. The observations were made in the open air at a dis- 
tance from my house : the compass-box was placed on a 
wooden tripod about 2 feet from the ground, and 5 feet from 
the north side of a garden wall, on which a wooden screen, 
moveable at pleasure, rested 3^ feet above the box. The 
following are the results which I obtained. 
Nature and Weight 
of the needle 
vibrated. 
No. of 
vibrations 
performed. 
Needle vibrated in the sun. 
Needle vibrated in the shade. 
Ter 
ex 
Extent of first 
vibration. 
Time. 
Terminal 
arc. 
Therm. 
Extent of first 
vibration. 
Time. 
Terminal 
arc. 
Therm. 
Magnetised 
steel, 
grains. 
Weight = 225 J 
IOO 
IOO 
IOO 
O O 
90 -f 90 
90 + 89 1 
9 ° + 89 1 
m. sec. 
5 554 
5 55-2 
5 55 - 1 
0 
20 
19 1 
» 9 i 
0 
IOO 
104 
I06 
O ° 
90 + 89 | 
90 + 90 
90 + 89 f 
m. sec. 
5 5 8 - 6 
5 5 8 - 8 
5 5 8 - 8 
0 
33 
33 1 
33 1 
O 
47 
48 
46 l 
Means 
9° + 89 f 
5 55-23 
19I 
io 3-3 
90 + 8 9 4 
5 5 8 -7 
33 h 
5°-5 
1st April, from 9 11 47 m to io h 15“. 
1st April, from io h 19“ to io h 45™. 
Glass, 
grains. 
Weight = 2241 
IOO 
IOO 
IOO 
90 + 88 
90 + 88 
90 + 88 
6 27.2 
6 27.1 
6 27.2 
17 
18 
i7 1 
96 
99 
IOO 
90 + 88 
90 + 88 
90 + 8 7 | 
6 27.0 
6 27.2 
6 27.1 
23 
23 
22 
49 
47 
47 
Means 
90 + 88 | 6 27.17 
J 7t 7 2 
9 8 -3 
90 + 88 
6 27.1 
22 §• 
47-7 
1st April, from io h 58^ to 1 i h 27“. 
1st April, from 1 i h 53” to o h 20 m ; 
Copper, 
grains. 
Weight = 543 
100 
100 
IOO 
9 ° + 93 
90 + 94 
9 ° + 93 l 
7 40.2 
7 40.2 
7 40.0 
24 
24 
24 
93 
98 
103 
9 ° + 93 i 
90 + 94 
9 ° + 93 1 
7 39 - 6 
7 39-4 
7 39-5 
3 ° | 
31 
31 
5 1 
49 s 
49 3 
Means 
90 + 93 | 
7 40 -I 3 
24 
98 
9 ° + 93 ! 
7 39-5 
3° 1 
50 
1st April, from i h 2o m to i h 53”. 
1st April, from 2a 5“ to 2h 35™. 
