Meteorological Essays and Observations. 345 
distances and resume their parallel progression. Tt would be difficult, 
I think, ‘to assign any other cause for this modification of ‘the phe- 
nomena than the one which has just been suggested. The evolution 
of heat, in the process of freezing, stops the decline of the tempera- 
ture in the regions exposed ‘to its influence, while it proceeds in those 
which are not exposed to the change; and the absorption of heat in 
the operation of thawing, prevents the accession of temperature which 
is due to the returning influence of the sun. When this operation has 
ceased, the vapour quickly attains its former relative degree of force. 
Wonderful adjustments these, to mitigate the rigours of 2 northern cli- 
mate! They both operate from November to February, by the evo- 
lution of heat in the coldest season of the year; and at the same time, 
by an extra supply of vapour, decrease the degree of dryness, and 
prevent the consumption of heat which always attends the process of 
evaporation.” P. 273. ‘ 
The next essay to which we shall draw attention relates to a subject 
of a more practical nature, and comprises some information of con- 
siderable utility to the meteorologist ; it is entitled, “ Remarks upon 
the Barometer and Thermometer, and the Mode of using Meteorological 
Instruments in general.” Than Mr. Daniell no one is more compe-~ 
tent to furnish valuable hints on this matter, from a considerable por- 
tion of his attention having been given to the manufacture of baro- 
meters. The Committee of the Royal Society, appointed to take 
into consideration the state of the meteorological instruments, did the 
author the honour to request him to attend to the construction of a 
new barometer for their apartments, and in the course of this inquiry 
he had, of course, an opportunity of making many extremely valuable 
practical observations. 
In the course of the experiments, he was led to a new method of 
filling the tube, of greater facility and correctness ; for the particulars 
of which we must refer to the book itself. It consists in conducting 
the process ix vacuo, and the author has but little hesitation in con- 
sidering it as accurate as the method of boiling, if performed with 
proper care, whilst it is infinitely less troublesome and hazardous. 
The electric light is as strong in the tube, and its appearance, in every 
respect, as perfect. 
The following remarks on the faulty construction of meteorological 
instruments in general, are extremely just and important. 
“* The generality of observers are but little aware of the serious 
inaccuracies to which those instruments are liable, In the shops of 
the best manufacturers and opticians I have observed that no two 
barometers agree ; and the difference between the extremes will often 
amount to a quarter ofan inch; and this with ail the deceptive ap- 
pearance of accuracy, which a nonius, to read off to the five hundredth 
part of an inch can give. The common instruments are mere play- 
things, and are, by no means, applicable to observations in the pre- 
sent state of natural philosophy. ‘I'he height of the mercury is never 
