Donovan — On alleged Imperfections of the Tuning-fork. 241 
applied to the upper teeth caused a loud ringing, and by far the loudest 
when applied to the canine tooth of the right side. After many 
ineffectual trials, I found that by allowing the vibrating fork to con- 
tinue in contact with this tooth during the continuance of its vibration, 
and concentrating my whole attention on the result, I could perceive 
a feeble beating as the ringing declined. By many repetitions my ear 
became better educated for perceiving the effect ; and after any violent 
exercise, as by running up and down stairs, the beating became a little 
more decided. So feeble was it at all times that it was with great 
difficulty I could fix my attention to perceive it at all. 
I tried several forks with the same results : so far they agreed with 
the statement of Earl Stanhope. But I soon observed that the inter- 
vals of time between the beats produced in the different forks were 
all exactly equal — a strange coincidence : for the fact implied that all 
the forks had been finished by the manufacturer to the exact same 
degree of inaccuracy. And what was more surprising was, that the 
fork, from which one quarter of an inch had been filed off gave 
exactly the same rhythm of beats as all the others. 
At this time I recollected that in tuning a violoncello, the instru- 
ment in proper position between the calves of both legs, and the in- 
terval between the third and fourth strings being more than a fifth, 
if the bow were evenly drawn across both strings, while at tlie same 
time the fourth string was very slowly screwed up, the cortfused sound 
of the impure fifth will gradually resolve itself into distinct beats, the 
intervals between which will become longer as the discord approaches 
a fifth ; and when a perfect fifth is attained, the fact is announced by 
a cessation of the beatings and the coalescence of the two sounds into 
a burst of perfect concord which no musician can ignore. The beat- 
ings, as they occur, will give an appulse to the calf of the right leg, 
which, if the player be attentive, he will feel, and by the cessation of 
the appulses, he will be advertised that his instrument is in tune, 
although he have not been watching the sonorous effect of screwing 
up the string. 
Earl Stanhope mentions a fact of the same character : he says that 
so small an alteration in the length of one of two strings as the yi o 
part of the one-hundredth of an inch produces an audible beating, when 
the strings are precisely of the same thickness : and not only the beat- 
ing may be heard, but what is remarkable, it may likewise be dis- 
tinctly felt. The best way to feel it is to support a small piece of 
steel wire, about two inches long, on the sound board of the mono- 
chord, with one of the finger nails. If the lower end of that piece of 
wire be semi- spherical ; if its upper end be pointed ; and if that pointed 
end be applied to the new or tender part of the nail, then the beating 
will be felt very sensibly." 
On one of these occasions, when I had exercised much with a view 
to perceiving the beatings of the fork more readily, I accidentally 
perceived that the beatings of my heart and the beatings of the fork 
applied to the canine tooth were synchronous. This observation 
R. I. A. PROC VOL. I.,'SBR. II., SCIENCE. 2 I 
