278  Dr.  A.  M.  Mayer's  Acoustical  Experiments 
5.  If,  with  the  aid  of  the  second  fundamental  principle  of  the 
mechanical  theory  of  heat,  we  calculate  the  modifications  under- 
gone by  the  electromotive  forces  of  contact  in  consequence  of  the 
increase  of  temperature,  we  obtain  results  which  do  not  agree  with 
experiment. 
XXXII.  Acoustical  Experiments  showing  that  the  Translation  of 
a  Vibrating  Body  causes  it  to  give  a  Wave-length  differing  from 
that  produced  by  the  same  Vibrating  Body  when  stationary. 
By  Alfred  M.  Mayer,  Ph.D.,  Professor  of  Physics  in  the 
Stevens  Institute  of  Technology,  Hoboken,  New  Jersey,  U.S. 
America*. 
The  Apparatus. 
FOUR  tuning-forks  mounted  on  resonant  cases  and  giving 
the  note  UT3,  =256  complete  vibrations  per  second,  were 
obtained.     I  will  designate  them  as  Nos.  1,  2,  3,  and  4. 
Nos.  1  and  2  were  brought  into  perfect  unison  by  a  process 
to  be  described. 
No.  1  was  placed  before  a  lantern ;  and  just  touching  one  of 
its  prongs  was  a  small  ball  (6  millims.  diameter)  of  good  cork, 
suspended  by  a  silk  fibre.  The  images  of  the  fork  and  of  the 
cork  ball  were  projected  on  a  screen. 
No.  3  had  one  prong  weighted  with  wax,  so  that  it  gave  2 
beats  a  second  with  No.  1  or  2. 
No.  4  had  the  ends  of  its  prongs  filed  off  until  it  also  gave  2 
beats  a  second  with  No.  1  or  2 ;  thus  No.  4  gave  2  vibrations 
a  second  more  than  No.  1,  while  fork  3  gave  2  vibrations  per 
second  less  than  No.  1. 
The  Experiments. 
In  the  experiments  1  to  7  inclusive,  No.  1  remains  before  the 
lantern  with  the  suspended  cork  ball  just  touching  one  of  its 
prongs. 
Exp.  1. — Fork  No.  2,  screwed  on  its  case,  was  held  in  the 
hand  at  distances  from  30  to  60  feet  from  No.  1  and  sounded ; 
the  ball  was  projected  from  the  prong  of  fork  1,  which  vibrates 
in  unison  with  No.  2. 
Exp.  2. — I  stationed  myself  30  feet  distant  from  fork  1,  and 
fork  No.  2  was  screwed  off  its  case  and  vibrated  in  one  hand 
while  the  case  was  held  in  the  other.  I  now  walked  rapidly 
towards  fork  no.  1 ;  and  after  I  was  in  regular  motion  I  placed 
the  fork  on  its  case,  and  just  before  I  ceased  walking  I  took  it 
*  Communicated  by  the  Author. 
