180 
T)R. E. P. PERMAN, DR. W. RAMSAY, AND MR. J. ROSE-INNES, 
Fig. 4. 
are altogether erratic, and this is to be expected, for it was not always possible so to 
rub the rod as to produce the required tone. A rod so placed is capable of many 
kinds of vibrations, and the particular rate of vibration, though the one most usually 
produced, may, by some difference in the method of rubbing, be I’eplaced by another. 
