528 



Mr. A. J. Ellis. 



[June 17, 



counted. Of thirty determinations of I thus made for the South 

 Kensington instrument,, the highest was 256*65, the lowest, 253'05, 

 and the mean, 255*85. Hence the value of I could apparently be not 

 far from 256, its nominal value. But when compared with an 

 Ut 3 of Koenig's, the reed beat 2*4 flat. Supposing Koenig's fork to 

 have been 256 truly, this made Appunn's Z=253'6, far less than any of 

 my counts and most of my calculations. Lord Rayleigh and Mr. R. H. 

 M. Bosanquet had already suggested to me that the confined air in the 

 box of the tonometer, and the vibration of the whole instrument 

 during the beats, "drew" the notes. I believe they thought that it 

 altered the pitch of the notes, and hence the number of the beats. I 

 began to entertain the same opinion, and devised the following ex- 

 periment, the Lords of the Committee of Council on Education allow- 

 ing me to remove the treble and tenor tonometers from South Kensing- 

 ton to the Museum of King's College, where Professor W. G. Adams, 

 E.H.S., allowed me to compare these instruments with those in the 

 Museum for many weeks. Suppose L, M, N", are adjacent reeds on 

 one instrument, and L', M', N' reeds of nominally the same pitch on 

 the other. Practically, they were not quite of the same pitch, a cir- 

 cumstance which showed inaccuracy of construction. Then I took 

 the beats between L and M, M and 1ST, and thus by addition obtained 

 the internal beats between L and N, that is, those which occurred 

 within the box of the tonometer. When I took the beats between L 

 and M', M' and N, and thus obtained the external beats between L and 

 N, that is, beats which were formed in the uncompressed atmosphere of 

 the museum external to the tonometers, the number of the internal 

 beats alio ays exceeded that of the external. On taking a mean of my 

 observations, which extended to every set of beats, I found that I 

 could reduce the internal to the external by diminishing the number 

 of the internal beats by 76 in 10,000. I was not completely satisfied 

 with the accuracy of my observations, or with what I considered the 

 rather hazardous mean, but was unable to repeat the very long course of 

 observations. In November, 1879, however, I was able to examine 

 every reed in all the tonometers by means of Scheibler's forks, and I 

 found that the nominal values of the reeds in the treble tonometer 

 could be reduced to those of the forks by a mean subtraction of 76 

 in 10,000 ; in the tenor tonometer (which was altogether flatter), by a 

 mean subtraction of 83 in 10,000 ; in the bass tonometer, octave 64 

 to 128, by a mean subtraction of 76 in 10,000 ; octave 32 to 64, of 64 

 in 10,000 ; octane 16 to 32, of 57 in 10,000 ; the octave 8 to 16 was too 

 uncertain to deduce a mean. These results singularly well confirm the 

 former. The nominal values had been deduced from observed internal 

 beats of reed with reed ; the external beats agreed whether they were 

 taken between reed and reed, or reed and fork. It is certain, there- 

 fore, that the internal beats were accelerated, whether the pitch, of the 



