522 
THE  ADMIEALTY  ASTEOXOHICAL  EXPEEIZSIEXT 
appears  in  average  weather  to  have  been  l°'l  greater,  and  the  depression  of  the  dew- 
point 1°  less  than  on  board  the  yacht.  Exceptional  weather  occurred  from  September 
13  to  September  20,  and  appears  to  have  been  in  connexion  with  the  Alta  Vista  storm 
of  the  14th,  though  not  in  exact  coincidence.  As  this  was  a period  dming  which  the 
computed  barometric  altitudes  of  the  mountain  station  gave  very  'wild  results  compared 
with  the  yacht,  we  have  computed  the  upper  observations  again  as  compared  with  Oro- 
tava ; but  the  discordances  are  even  greater,  as  the  enclosed  numbers  ^V11  show,  and 
they  are  evidently  in  connexion  with  the  same  general  disturbances  of  the  atmosphere, 
thereby  reflecting  credit  on  both  the  lower  observers. 
Date. 
Height  of 
Alta  Vista 
above  Orotava. 
Correction 
to  mean. 
Height  of 
Alta  Vista 
above  yacht. 
Correction 
to  mean. 
feet. 
feet. 
feet. 
feet. 
1856,  Sept.  1. 
10,672 
— 
30 
10,704 
- 10 
2. 
10,680 
— 
38 
10,715 
- 21 
3. 
10,695 
— 
53 
10,731 
- 37 
4. 
10,715 
— 
73 
10,768 
- 74 
5. 
10,699 
— 
57 
10,754 
- 60 
6. 
10,695 
— 
53  1 
10,726 
1 0,666 
- 32 
8. 
10,618 
+ 
24 
+ 28 
9. 
10,627 
+ 
15 
1 0,656 
+ 38 
1 1. 
10,646 
— 
4 
10,708 
— 14 
12. 
10,6i0 
— 
38 
10,747 
— 53 
13. 
10,692 
— 
50 
10,758 
- 64 
15. 
10,534 
+ 108 
10,597 
+ 97 
16. 
10,559 
+ 
83 
10,617 
+ 77 
17. 
10,482 
+ 160 
10,562 
+ 132 
Boiling-iJoint  Thermometer. 
A boiling-point  thermometer,  made  by  Mr.  Adie  of  Edinburgh,  graduated  to  tenths, 
and  reading  to  hundredths  of  a degree,  and  since  admirably  tested  by  my  friend 
Mr.  Welsh  of  the  Kew  Observatory,  was  observed  Avith  at  Guajara,  Alta  Vista  and  the 
Peak,  but  not  so  often  as  I see  would  have  been  desirable;  so  that  I can  only  now 
state  that  for  approximative  purposes  Captain  Boileau’s  Tables  are  most  satisfactory, 
giving  by  two  observations  the  height  of  Guajara  subject  to  a correction  of  +40  feet. 
Alta  Vista  +70,  and  the  Peak  —26;  the  corrections  of  simultaneous  barometrical 
altitudes  being  +122,  +98,  and  — 2 feet. 
(6.)  Perijtatetic  Ohsermtions. 
In  all  the  journeyings  up  and  down  the  mountain,  the  altitudes  were  measured  by 
myself  with  a sympiesometer,  especially  made  for  the  occasion  by  Mr.  John  Adie. 
From  the  simultaneous  readings  of  this  instrument  with  the  barometer  at  Orotava. 
Guajara,  and  AltaVista,  a temperature  and  an  altitude  correction  have  been  made  out. 
and  have  been  applied  in  every  case  to  reduce  the  sympiesometer  readmg  to  what  our 
barometer,  corrected,  would  have  sho^vn  at  the  same  place  and  time.  The  calculation 
of  the  height  was  then  performed  as  with  a barometer  reading.  The  height  so  found 
