IN METEOROLOGICAL REGISTRATION. 79 
the effects of daily changes may be traced better than those 
of annual ones. The atmosphere is disturbed by solar influ- 
ence every hour of the day, and these disturbances take place 
so regularly as to admit of their being followed and minutely 
examined, with a view to discover the precise way in which 
the solar influence is exerted. The daily changes therefore 
afford better means than the annual ones of inquiring into 
the causes of atmospheric disturbance. In most parts of 
the world, the atmosphere becomes heavier from four until 
ten o’clock in the morning, during which time the baro- 
meter rises; and the causes that must then have been in 
in action to produce these effects, being so regular, may be 
followed, and the forces may possibly be exhibited. This 
has been attempted for a considerable time, but the results 
obtained are by many persons deemed unsatisfactory ; it 
therefore becomes desirable that we should examine the 
means that have been employed to account for barometric 
movements, and if they should be found to have been 
defective, to point out their defects and suggest improve- 
ments. 
With the approach of the sun every morning, evapora- 
tion of water from the part of the earth’s surface heated 
by it becomes more active, and additional aqueous vapour 
is sent into the air, showing itself in a higher dew- 
point and an increase of atmospheric pressure, which of 
course raises the mercury of the barometer. The hours 
during which these phenomena occur vary to a certain 
extent with latitude and season, but the average time 
is from four to ten o’clock in the morning, and within 
that period the barometer rises in consequence of an 
increase of aqueous vapour. At a certain time, how- 
ever, say ten o’clock, the barometer begins to fall, although 
vapour continues to pass, even in greater abundance, into 
the atmosphere. In the present state of our knowledge 
of the subject we naturally ask, What can be the cause 
