OF DENISON UNIVERSITY. 
19 
2. A Simple Chronograph. 
The apparatus illustrated onPlate B, Fig. 4, can be made in any 
laboratory, and is for many purposes a good substitute for an expen- 
sive chronograph governed by clock work. It consists of an electrical 
pendulum <2, suspended on a steel knife edgey which makes and breaks 
circuit by carrying a platinum wire through a drop of mercury at A 
The same circuit contains an ordinary telegraph sounder with a long 
bent wire attached, so that every depression of the armature makes a 
dot on a long strip of smoked glass, which can be drawn slowly along 
the table in front of it. A large turning fork, carrying a short piece 
of very fine wire as a stylus, makes a tracing, simultaneously, about 
one half a centimetre to one side. This fork is conveniently support- 
ed by being inserted into one end of a piece of wood e, which is 
hinged at y, to the table. The amount of pressure of the stylus is reg- 
ulated by a wooden screw passing through c, and pressing against the 
table. If the pendulum is adjusted to beat seconds and vibrated 
through a rather large arc so that the sounder works with a sharp, short 
click, the period of the fork may be very accurately determined. The 
close agreement of a number of independent determinations indicates 
the accuracy of which the method is capable. This is shown in the 
following series of four successive experiments : — 
Experiment. 
Times. 
Vibrations. 
Vibrations per Sec, 
I 
8 sec. 
440.7 
55-09 
2 
6 “ 
330-2 
55-°3 
3 
6 “ 
330.6 
55-10 
4 
5 ‘‘ 
275-1 
55-02 
Average number of vibrations per second, 55- 06 
If it is desired to measure any other short interval, having thus 
accurately determined the period of the fork, it is only nece^ssary to 
stop the pendulum, so as to complete the circuit permanently, and 
then introduce a telegraph key into the line. Now the sounder will 
register accurately each time the key is depressed, and the time be- 
tween any two depressions may be determined by counting the num- 
ber of fork vibrations included between the dots corresponding to 
those depressions. If for any reason it is desired to have the seconds 
marked also, the key for the occasional signals must be included in a 
