1G8 
CAPTAIN ABNEY ON THE SENSITIVENESS 
Table VI.—Extinctions with Apertures of Different Sizes. 
i 
E light. 
1 
E light. 
1 
1 - 
1 
; Diameter. 
1 
Diameter in 
po-vvers of 2. 
Reading. 
Log. 
Diameter. 
Diameter in j. 
- o Reading, 
po-^vers or 2. ° 
Log. 1 
1 
inches. 
i 0725 
! 0-42 
1 0-30 
1 017 
0-086 
0-036 
-0-48 
-1-25 
-1-74 
-2-56 
-3-56 
-4-81 
331 
285 
255 
209 
163 
85 
117 
1- 55 
1-81 
2- 20 
2-60 
3-27 
inches. 
0-94 
0-725 
0-525 
0-42 
0-35 
0-30 
0-170 
0-086 
0-036 
0-012 
—0-09 above 360 
-0-48 
-0-93 352 
-1-25 3.35 
-1-52 3-23 
-1-74 303 
-2-56 255 
— 3-56 195 
-4-81 123 
-6-40 39 
1-00 
1-12 
1-22 
1- 39 
1-81 
2- 32 
2- 94 
3- 67 1 
1 
C light. 
0-725 
0-525 
0-42 
0-35 
0-30 
0-170 
0-086 
0-036 
0-012 
-0-48 
-0-93 
-1-25 
-1-52 
-1-74 
-2-56 
-3-56 
-4-81 
-6-40 
340 
325 
312 
300 
275 
230 
178 
100 
15 
1-076 
1-20 
1-30 
1-42 
1- 63 
2- 02 
2- 57 
3- 14 
3-85 
D light. 
2-00 
1-50 
0-94 
0-725 
0-30 
0-170 
0-086 
0-036 
[ 
+ 1-0 335 
+ 0-6 3.32 
-0-09 325 
-0-48 300 
-1-74 223 
-2-56 185 
-3-56 132 
-4-81 55 
1-12 
1-13 
1-20 
1- 42 
2- 08 
2-40 
2- 87 
3- 51 
E light. 
2-00 
+ 1-0 
315 
1-29 
1-50 
+ 0-6 
315 
1-29 
0-94 
-0-09 
303 
1-39 
0-525 
-0-93 
245 
1-89 
0-42 
-1-25 
234 
1-98 
0-35 
-1-52 
220 
2-11 
0-30 
-1-74 
200 
2-28 
The indications here given are that (fig. 5) the curves with apertures less than 
inch diameter become straight lines, all of which are parallel, and it is somewhat 
remarkable that from that point the intensity of a light which will be just extin¬ 
guished with a certain diameter of aperture may be increased 10 times, and yet 
be invisible when an aperture with of that diameter is employed ; if the intensity 
of the light be increased 100 times, we have only to diminish the diameter of 
the aperture to and it will again disappear. (It may be noted that in the 
lowest curve the dotted portion is taken from the two top curves.) The equation 
connecting the two has the form of I = where m is detennined by the slope of 
the line and the log 2. 
We shall see further on that connection between the intensity of the light 
