Records of the Free Vibrations of a Tuning-fork. AAT 
The contact of a rigid platinum point being found to inter- 
fere too much with the motion of the membrane, the point was 
attached to one end of a light spring about 115™™ long, the 
other end of which is soldered to the lever Q. The spring is 
made by flattening a piece of copper wire. It lies close to the 
lever and has very little play, but answers its purpose perfectly. 
It may be thought that the relay X might be dispensed with, 
the battery B” being made to record directly through the pen 
- By the use of the relay, however, the dash made by the 
pen H at each beat, can be reduced to any convenient length; 
and besides, the distinct clicks of the relay at the beats, are 
much easier to observe than the beats themselves, particu- 
larly when these are not more frequent than two or three to 
the second. The variations in the rate of these clicks give 
clear indications of changes in the rate of the siren, and their 
cessation shows when the excursions of the membrane are too 
small to cause a record of the beats. 
in front of the roller. Of course the roller and all the contact 
points must be kept clean. : 
Care must be taken that the armature A, while very close to 
the poles of the magnet, shall not touch them, otherwise the 
residual magnetism will retard its release. I find it most con- 
venient to place the plane of the mouth of the resonator nearly 
parallel to the plane in which the fork vibrates, as the resona- 
tor is then not in the way of the bow. The best effect of the 
fork in producing beating vibrations of the membrane occurs, 
however, when the opening of the fork is not exactly in front 
depends on the distance of the siren. The t position is 
found by sounding the siren and the fork, and moving the 
which gave the best results, the center of the siren was 80™" in 
front of the plane of the mouth of the resonator and 50™ to 
the right of the center of the mouth, while the center of the 
fork was 20" in front of the plane of the mouth, and 50™™ to 
the left of it. : 
