428 SCIENCE. [N.S. Vou. X. No. 248, 
TABLE IV. 
Horizontal Settings. Vertical Settings. 
(The readings show deviations from level.) (The readings show deviations from verticality.) 
nine he The BLED with ih The avery 
-| a 
Observer. tthe of || algebraic- | algebraic: | «. sa caet “tion of | ne algebraic: Blgsouiics “ aaiies plence 
HORE Os praallest lateet of the wea He eeu Or paileee eee orbs ieee 
readings. Treading. | reading. readings. Miva readings. renaine! aratinre readings. hes 
f | mean. mean. 
1 —1°.19 || —1°.48 | —0°.85 0°.63 0°.21 || —1°.02 || —1°.39 | —0°.55 | 0°.84 0°.21 
2 —0 .16 |} —1 .00 | +0 .62 1 .62 0 .32 |; —O .03 |} —0 .98|} +0 .64| 1 .62 0 .36 
3 —0 .44 || —1 .10 | +0 .32 1 .42 0 .32 || —O .55 |} —1 .70| +0 .28] 1 .98 0 .33 
4 —O .10 |} —1 .41 | +1 .10 2 .51 0 .48 || —1 .59 || —3 .10| —O .50| 2 .60 0 .62 
5 +0 .26 || —O .53 | +1 .07 1 .60 0 .33 || +1 .29 || +0 .42/ +2 .36) 1 .94 0 .42 
6 —1 .22 || +2 .13 | —O .50 1 .63 0 .32 || —O .59 ||} —1 .37|/+0 .05|] 1 .42 0 .29 
7 —0 .44 || —O .90 | —O .02 0 .88 0 .25 || —O .46 ||} —1 .56/-+0 .42/ 1 .98 0 .44 - 
8 —0 .81 || —1 .50 | —0 .30 1 .20 0 .24 || —O .30 || 0 .70|+0 .06| 0 .76 0 .20 
9 —O0 .38 || —1 .12 | +0 .04 1 .16 0 .24 +0 .42 || —O .26| +1 .08| 1 .34 0 .32 
10 +0 .00 || —O .72 | +0 .60 1 .32 0 .26 +0 .08 || —0 .70| +0 .95| 1 .65 0 .53 
11 +0 .56 || —O .45 | +1 .40 1 .95 0 .33 || —O .33 ||} —1 .08/} +0 .38| 1 .46 0 .36 
12 —0O .11 || —1 .00 | +0 .55 1 .55 0 .37 || —0 .10 |; —O .83 | +0 .67| 1 .50 0 .25 
13 —0 .23 || —1 .30 | +0 .57 1 .87 0 .39 || —O .10 |} —1 .07| +0 .83| 1 .90 0 .44 
14 —O0 .01 || —O .64 | +0 .57 Thea 0 .24 +0 .50 || —O .17| +1 .48| 1 .65 0 .34 
15 +0 .01 || —O .76 | +0 .65 | 1 .41 0 .27 || —O .09 || —1 .25|+0.70| 1 .95 0 .38 
16 +0 .17 || —2 .03 | +2 .02 4 .05 0 .01 —1 .41 || —2 .89| +1 .62| 4 .51 0 .67 
17 +0 .42 || —O .11 | +0 .92 1 .03 0 .23 +0 .77||—0 .17| +1 .61| 1.78 0 .37 
18 +0 .81 +0 .35 | +1 .52 ib gales 0 .27 || —0 .05 0 .65; +1 .30| 1 .95 0 .50 
19 +0 .28 || —0O .98 | +1 .82 2 .80 0 .69 || —O .32 |; —1 .78| +0 .77} 2 .55 0 .49 
20 —0 .16 || —O .80 | +0 .80 1 .60 0 .27 +0 .64 |} +0 .01| +1 .48] 1 .47 0 .41 
21 +0 .18 || —O .62 | +0 .85 1 .47 0 .29 +0 .01 || —O .77| +0 .76/ 1 .53 0 .26 
22 —0 .04 || —O .64 | +0 .43 1 .07 0.17 || +0 .02 || —O .30/+0 .44| 0 .74 0 18 
23 +0 .19 || —O .60 | +0 .86 1 .46 0 .33 +0 .33 || —O .62) +1 .15) 1 .77 0 .49 
24 +0 .04 || —1 .43 | +1 .60 3 .03 0 .65- || —O .67 || —2 .27| +41 .44| 3.71 0 .67 
25 —0O .86 || —3 .71 | +1 .87 5 .58 1.39 || —O .81 ||} —4 .01/ +4 .05| 8 .09 0.7% 
26 —0 .45 || —2 .52 | +1 .81 4A .33 0.71 —1 .55 || —3 .40| —0 .37| 3 .03 0 .61 
27 +1 .16 +0 .65 | +1 .56 0.91 0 .16 +0 .97 || +0 .68| +1 .35| 0 .67 0 .13 
28 +0 .39 +0 .01 | +0 .79 0.78 0 .20 || —O .07 || —O .52| +0 .35| O .87 0 .16 
29. —0 .38 || —1 .60 | +0 .50 2 .10 0 .58 || —O .59 || —1 .19| +0 .20/} 1 .39 0 .36 
With this apparatus many hundreds of in Harvard University, or other members of 
settings were made. Table IV. contains 
the results of a large number of these made 
by 29 different persons, each one of whom, 
while making his long set of observations, 
stood at ease in front of the tube and, using 
both eyes, attempted toset the line correctly. 
All the angles are here given, as they were 
first read, to hundredths of a degree, but it 
is evident that the last figure is generally 
nearly meaningless. Of these 29 persons, 
two (Nos. 25 and 26) are boys 10 and 8 
years old, respectively, and -No. 16 is a 
somewhat older boy. Nos. 23 and 24 are 
young girls. The ranges of four of these 
five children are noticeably large. No. 21 
is alady. ‘Thirteen of the other observers, 
all of whom are men, are either instructors 
_ the staff of the Jefferson Physical Labora- 
tory. It should be said that a given number 
may represent different observers in the 
different tables. . 
Eleven of the twenty-nine subjects were 
known to be astigmatic. Most of these 
could see very imperfectly without eye- 
glasses, and yet they could set the line about 
as accurately without these glasses as with 
them. For instance, the means of horizon- 
tal and vertical settings made by observer 
No. 13 without his spectacles, were — 0°.20 
and + 0°.02 respectively. There does not 
seem to be any obvious connection between 
the directions of the principal axis of the 
eyes of an astigmatic observer and the bias, 
shown by his observations, 
