VELOCITY AND PEESSUEE INSTRUMENTS. 
373 
Clock Keadings.—Experiments with 38-ton, 12-in. Gun. 
Round No. 14. 
Observed time, 
secs. 
1st observation 1000 revolutions made in . 32-0 
2nd n a . 31’9 
3rd h ,i . 31-8 
Round No. 15. 
1st observation 1000 revolutions made in . 32*0 
2nd ,i „ . 31*9 
3rd i, „ . 31*9 
Round No. 16. 
1st observation 1000 revolutions made in . 31*5 
2nd i, « .. 31*7 
3rd i, a . 31-6 
Round No. 17. 
1st observation 1000 revolutions made in . 31*5 
2nd a n . 31'4 
3rd „ « . 3T5 
Round No. 18. 
1st observation 1000 revolutions made in . 31*6 
2nd n i, . 31*6 
3rd n a . 31*6 
Round No. 19. 
1st observation 1000 revolutions made in . 32*0 
2nd i, ,i . 32*1 
3rd „ i, . . 32*2 
The maintenance of the speed with so great a degree of uniformity, is 
obtained by means of very great accuracy of workmanship in all parts of the 
mechanism. 
The arrangements for obtaining the electrical records are as follow:—The 
edges of the revolving discs are covered with smoke by means of an oil lamp, 
and are connected with one of the secondary wires, G (Fig. 1) of an induc¬ 
tion coil. The other secondary wire, H, carefully insulated, is brought to a 
discharger, 7, opposite the edge of its corresponding disc, and is fixed so as 
to be just clear of the latter. 
When a spark passes from the discharger to the disc, a minute portion of 
the lamp-black is burnt away upon that part of the disc which was opposite 
to the discharge at the instant of the passage of the spark. A distinct spot 
is left on the blackened disc, the lamp-black at that point having been burnt 
away by the spark, so that the metal is shown beneath. 
The mode of connecting the primary wires of the induction coils with the 
bore of the gun in such a manner that the shot, in passing a defined point, 
