Lectvres  on  Ac/ricultural  Chemistry . 
of  publication,  but  is  now  out  of  date.  The  doctrine  of*the 
circulation  of  sap  is  stated  according  to  the  theory  and  ex]>eri- 
ments  of  j)revious  iiupiirers,  chiefly  those  of  Grew  and  Mirbel. 
In  this  lecture  Davy  utilised  his  own  researches  on  the 
abundance  of  silicious  matter  in  the  ejuderniis  of  certain  plants, 
a })aper  to  which  reference  has  already  been  made. 
The  fourth  lecture,  on  “ Soils  and  their  Analysis,”  is  a 
valualde  essay,  on  the  merits  of  which  all  critics  are  united. 
Dr.  Paris  describes  it  as  the  most  original  and  Aaluable 
divisions  of  the  work,  and  Professor  Warington  as  “ one  of 
his  best  lectures,  full  of  keen  observation  and  suggestive 
experiment.”  The  relations  of  different  soils  to  heat  and 
moisture  are  here  discussed.  The  im])ortance  of  a knowledge 
of  the  primary  rocks  is  ])ointed  out,  but  it  must  be  remembered 
that  geology  has  become  a more  formal  science  since  this 
lecture  was  written.  The  analysis  of  soils  was  originally  looked 
upon  as  the  most  important  part  of  the  lecture,  but  other 
classifications  have  since  been  adopted. 
The  fifth  lecture  deals  with  “ The  Influence  of  the  Atmo- 
sphere on  Vegetables,”  and  the  question  whether  plants  in 
general  have  any  material  effect  in  j)urifying  the  air  is 
discussed.  Davy  disagreed  with  the  conclusions  of  Mr.  D. 
Ellis  in  his  researches  on  this  subject,  but  an  Edinburgh 
Reviewer  argues  in  favour  of  Ellis’s  views.’ 
The  sixth  and  seventh  lectures  are  devoted  to  the  question 
of  manures  ; the  former  with  those  of  vegetable  and  animal 
origin,  and  tbe  latter  with  those  of  mineral  origin — the  most 
important  of  all  the  branches  of  agricultural  chemistry,  but 
one  in  which  knowledge  has  advanced  so  greatly  that  these 
cha])ters  are  now  comparatively  of  little  value. 
The  eighth  and  last  lecture  refers  to  “ Burning  Lands, 
Fallowing,  and  the  Rotation  of  Crops.”  The  author  shows  that 
while  stiff  clays  are  improved  by  burning,  barren  and  sandy 
soils  have  sometimes  been  injured  almost  irrecoverably  by 
burning.  This  concluding  lecture  also  contains  many  observa- 
tions of  value  on  several  agricultural  o])erations. 
The  appendix  on  the  food  of  animals,  consisting  of  a series 
of  experiments  on  the  nutrient  matter  afforded  by  grasses, 
carried  out  at  Woburn  by  order  of  the  Duke  of  Bedford,  was 
described  in  Ibll  as  very  copious  and  valuable,  but  it  was 
omitted  from  Skier’s  edition  of  the  lectures  (Ib-KI)  as  out  of 
date. 
Edinhnrgh  lieview,  Vol.  22,  page  251. 
