338 
MR. J. WELSH’S ACCOUNT OF METEOROLOGICAL 
point of complete saturation. After leaving the cloud the humidity diminished 
steadily but not very rapidly till 5300 feet, where a slight rise commenced, continuing 
till 6700 feet; it then decreased till 8300 feet, when it rose again and remained 
nearly constant at 70 for the last 3000 feet of the ascent. The changes occurring in 
this series were neither to the same extent nor so abrupt in their character as those 
shown in the first two. 
November 10.~The humidity, again, as in all the previous series, increased from the 
earth to the first cloud, which was at a low elevation and of but little density ; upon 
leaving it, at about 1900 feet, a slight depression took place. Immediately above this 
low cloud a different current of air existed, shortly after entering which the humidity 
again increased until, in the second cloud, it became nearly complete ; the decrease, 
after leaving the cloud at 5000 feet, becoming rapid and attaining a minimum at 
6500 feet. A second well-defined maximum was reached at 8300 feet, followed at 
10,000 feet by a secondary minimum. The humidity diminished on the whole till 
about 15,800 feet, when a sudden increase commenced, which continued from 16,o00 
to 17,600 feet, followed by an equally sudden decrease at 18,000 feet, the humidity 
subsequently increasing. The fluctuations in this series were numerous, there having 
been no fewer than four or perhaps five different strata of vapour. 
7* General Remarks. 
The principal results deduced from the experiments described may be thus gene- 
rally stated. . , , , 
The temperature of the air decreases uniformly with the height above the ear i s 
surface, until at a certain elevation, varying on different days, the decrease is 
arrested, and for a space of from 2000 to 3000 feet the temperature remains nearly 
constant, or even increases by a small amount ; the regular diminution being after- 
wards resumed and generally maintained, at a rate slightly less rapid than in the 
lower part of the atmosphere, and commeneing from a higher temperature than 
would have existed but for the interruption noticed. This interruption in the 
decrease of temperature is accompanied by a large and abrupt fall in the temperature 
of the dew-point, or by actual condensation of vapour, from which it maybe inferre. 
that the disturbance in tbe progression of temperature arises from a development 
of heat in the neighbourhood of the plane of condensation. The subsequent falls in 
the temperature of the dew-point are generally of an abrupt character, and corie- 
sponding interruptions in the decreasing progression of temperature are sometimes 
distinguishable, but in a less degree ; as might indeed be expected from the fact, that 
at lower temperatures the variations in the absolute amount of aqueous vapour are 
necessarily smaller, and their thermie effects consequently diminished. 
