REPORT ON METEOROLOGY. 
237 
Tables ; but the means of measuring the force of vapour with 
accuracy being only lately attained, the due correction has but 
within a few years become an object of adequate attention. Dr. 
Anderson, who has bestowed great attention upon the subject 
of Hygrometry, wrote a paper on this correction a few years 
ago *. Mr. Galbraith, in his Mathematical and Astronomical 
Tables , has followed Dr. Anderson in giving the correction, 
and has facilitated its application by the use of Tables. 
Considering the problem as one of the highest interest accu¬ 
rately to solve, we approve of the introduction of every correc¬ 
tion established upon sound theory and accurate experiment 
conjoined, even though in amount it may be less than the errors 
of observation or the unavoidable uncertainties arising from 
the interference of imperfectly understood active causes. By 
this process uncertainty will gradually be cleared away; and 
though there will undoubtedly be a limit beyond which no 
human perseverance can carry the approximation to truth, and 
a much wider one within which not one observation in a hun¬ 
dred will come, yet still truth will be separated from error, and 
the actual anomalies unaccounted for will be eliminated with 
precision. We do not therefore blame the superfluous accuracy 
(practically considered,) at which the formula of Laplace appears 
to aim. And for every-day observations it is easy to substitute 
those simple expressions which in most cases will give almost as 
good an approximation to the truth j*. But in all experimental 
investigations where the arrival at truth within certain limits is 
the object, too great care can hardly be taken to avoid the intru¬ 
sion of causes always acting in one direction , or which in the 
mean of a number of observations do not compensate them¬ 
selves. Such, in fact, are some of the minuter corrections of 
Laplace, as those for latitude and for diminished gravity in a 
vertical direction. 
The configuration of the ground has a considerable effect on 
the measurement of heights by the barometer, as has also the 
season of the year and time of the day. This last point has 
lately been a more especial subject of attention, although along 
with the former it w r as investigated by Ramond with his usual 
assiduity, who pointed out noon as the best hour for the ex¬ 
periment. It is very clear that the horary oscillation will in the 
first place affect the barometric measurement, but this is in 
Europe a very minute quantity and easily allowed for. At the 
equator, being almost the only variation to which the mercurial 
* Edinburgh Philosophical Journal, vol. xii. xiii. 
j* Among the numerous forms which these have received, there is perhaps 
none more comprehensive and satisfactory than that given by Mr. Baily in his 
most valuable portable volume of Astronomical Tables, Lond. 1827. 
