AT NIGHT, FROM THE EARTH, ETC. 
127 
horizon, the heat emitted by it to the earth will overbalance that which the earth 
radiates upwards ; at times however, in places shaded from its direct beams, the 
amount of heat radiated exceeds that received from the sun and all other sources, 
and dew will be continually deposited throughout the day. Some instances of this 
are exhibited in the following Tables. 
In taking these observations I have been much assisted by my then colleagues in 
the Magnetical and Meteorological Department of the Royal Observatory, viz. 
Messrs. Dunkin, Hind and Paul: these gentlemen frequently, on my commencing a 
series of observations, continued them as long as circumstances required, or they 
have begun a series which were continued by myself ; and whenever any doubt 
attached to the readings from the unexpected lowness of the thermometers or other 
causes, they were always confirmed by one or other of these gentlemen, and after- 
wards by an interchange of instruments. 
I have also to acknowledge my obligations to the Astronomer Royal for his kind- 
ness in permitting me to carry on these experiments within the grounds of the Royal 
Observatory; also for providing me with a skeleton form in which the observations 
were registered; and also for inclosing the piece of ground within which the regis- 
tering instruments were placed. 
The whole of the calculations have been twice performed by myself at different 
times, and parts of them, which appeared to be more liable to error than others, have 
been examined by another person. I believe, therefore, the whole to be nearly correct. 
Section I. — Results of Simultaneous Observations made by Mercurial Thermometers, 
not self -registering. 
The first process in the reduction of these observations, was to take the difference 
between the reading of the thermometer, freely suspended in air, at the height of four 
feet, and protected from the effects of radiation, and the simultaneous reading of every 
other thermometer. 
The next process was to divide these differences into groups, arranged according to 
the excess of the reading of the thermometer, suspended in the air, above that placed 
on long grass. 
The next step was to collect all these differences under the head of their respec- 
tive substances for every degree of such excess of air temperature above that of long 
grass temperature. 
The next step was to arrange these numbers according to the dates of their occur- 
rence, and to write out abbreviative remarks which were made at the time of obser- 
vation ; and in this way the following Tables have been formed. 
Tables I. to XVI. contain the results deduced from the observations taken be- 
tween 1843, September 13, and 1843, November 15 ; Tables XVII. to XXVIII. con- 
tain the results from the observations taken between 1843, November 16, and 
December 31 ; and Tables XXIX. to XLIV. contain those from observations taken 
between 1844, January 1, and 1844, May, 1. 
MDCCCXLVII. S 
