6 
POPULAR SCIENCE REVIEW. 
nearly uniform velocity, and recording clock-beats as well as 
screen-striking within the 2,000th of a second (the projectile 
nutting the threads of ten or fifteen successive screens, placed 
50 — 150 feet apart), gives a permanent comparative record of 
the instants of the passage of the ball. The following example 
is expanded from “ Trans, of the Eoyal Society,” 1868, p. 425. 
Hemispherical-headed shot. Diameter 4-7 in. $ weight 39-34 lbs. 
CLOCK 
Time 
Reading j 
Un corrected Reading 
A, 
a 2 
a 3 
1 " 
4-910 
+ 15-910 
2 " 
20-820 
+ 15-830 
-80 
+ 40 
3 " 
36-650 
+ 15-790 
-40 
-50 
4" 
52-440 
+ 15-700 
-90 
+ 40 
5" 
68140 
+ 15-650 
-50 
6" 
83-790 
CLOCK 
Time 
Reading 
Corrected Reading 
Ai A 3 A 3 
4-91 
4 ' 910 15-910 7f) 
2 " 
20-82 
20-820 16 , 840 3 
3 " 
36-65 
“ 15-773 2 3 
4" 
52-44 
62 ' 433 15-709 !: 3 
5" 
68-14 
68 ' 142 15-648 
6" 
83.79 
83-790 
By interpolation * the instant of passing ten screens in suc- 
cession, as marked by the spiral traced on the revolving drum, 
is thus given in decimals : — 
Times oe Passing the Screens. 
■ 
Screen 
1 1 2 
3 
4 | 5 
6 
7 1 8 
9 
10 
Times 
2"-4692 2" "5956 
2"-7238 
2 
'•8539 2 //, 9858 
3"-1196 
3 
•2552 3''-3925 
3"-5315 
3"-6722 
A t 
1264 1282 1301 
1319 1338 1356 
1373 1390 1407 
a 2 
18 
19 
18 19 
18 
17 17 
17 
a 3 
+1 
1 
+1 
L 
1 
0 0 
The length of the spiral traced on the paper cylinder is 
about nine or ten inches for one second ; thus by a vernier and 
* It is hardly desirable to insert the formulae of this process in an article 
on Popular Science. 
