Pyrometry  and  Areometry , See.  453 
heatw:  the  quicker,  however,  the  returns,  the  more  re- 
gular they  were;  it  will  be  therefore  only  from  fuch  as 
were  quick  that  I fhall  hereafter  deduce  my  conclufions. 
Another  difficulty  I met  with  in  my  experiments  arofe 
from  the  difference  of  the  effebt  of  the  different  changes 
of  the  temperature.  When  I fuddenly  changed  the  tem- 
perature of  the  water  from  io°  to  70°  of  the  Thermo- 
meter to.  which  I have  given  the  name  of  common  in  my 
work  upon  the  Modifications  of  the  Atmofphere  (which 
anfvver  to  54°^  and  189!.  of  Fahrenheit)  a fomewhat 
lefs  length  of  brafs  was  wanted  to  compenfate.  the  dilata- 
tion of  the  glafs,  than  when  I increafed  the  heat  lefs;  as, 
(d)  Since  the  writing  of  this  I have  been  told,  that  the  fame  phenomenon  is 
obferyed  in  the  correcting  Thermometer  of  watches; , and  that  it  produces^  irregu- 
larities which  are  in  an  increafing  progreffton,. 
for 
3eur  (d).  Qnand  ces  retours  etoient  prompts  ils  etoient  plus  reguliers.  Ce  ne 
fera  done  que  de  celles  de  mes  obfervations  qui  furent  promptes,  que  je  tireraT 
ct-apris  les  refultats  probables, 
Un  autre  embarras  que  j’eprouvai  dans  ces  experiences,  provintde  la  difference 
d’effet  des  changemens  differens  de  temperature.  Quand  je  portois  tout  a coup 
la  temperature-.de  mon  eau  de  io°  a 70°  du  Thermometre  que  j’ai  appel’e  com - 
mun  dans  mon  ouvrage  fur  les  Modifications  de  i’ Atmofphere,  et  qui  correfpondent 
a.54°|  et  i8g°|.de  Fahrenheit,  il  me  failloit  une  longueur  un  peu  moindre  de 
leton  pour  compenfer  la  dilatation  du  verre,  que  lorfque  j’augmentois  moins  la- 
(d)  J’at  appris  depuis  que  j’ai  ecrit  ceci,  qu’on  remarque  ce  phenomene  dans  les  Thermometres  cor- 
gefteurs  dcs  mojjtres,  et  qu’il  y caufedes  irregqlarites  croiflantcs. 
chaleuiy 
