lvi INTRODUCTION TO THE MAKERSTOUN OBSERVATIONS, 1845 AND 1846. 
The observations of the dry and wet bulb thermometers, given in this volume 
are not corrected for the errors of the thermometers; but the corrections have been 
applied to the abstracts of results. 
92. The maximum and minimum self-registering thermometers, on RuTHER- 
FORD’s construction, were made by Aprz and Son; they were attached to a frame 
fixed to the north side of the Observatory, about three feet from the ground, and 
near the dry and wet bulb thermometers. A self-registering mercurial thermome- 
ter, with a black bulb, by R. Apre, of Liverpool, was placed, in the end of May 
1844, within the enclosed space occupied by the Observatory rain-gauge, exposed 
to the sun, for the purpose of obtaining the maximum amount of solar radiation ; 
another self-registering alcohol thermometer, with black bulb, by the same maker, 
was placed near the other in September 1844, with its bulb in the focus of a para- 
bolic metallic reflector, for the purpose of obtaining the minimum of terrestrial 
radiation. The observations of the self-registering thermometers have all been cor- 
rected for the scale errors of the thermometers. The observations of the minimum 
thermometer for the temperature in the shade are apparently in all cases from 1° to 
2° less than the lowest temperature indicated by the dry bulb thermometer; the 
difference, it is believed, is due to the greater exposure of the minimum thermo- 
meter to radiation and deposition of dew. 
93. Another thermometer was employed for the determination of the tempera- 
ture of the water in two pump-wells, which are within about 200 yards of each 
other; the pumps are nearly on the same surface-level, the depth of the cottage- 
well being 10 feet,—that of the garden-well 21 feet. On one occasion, it was found 
that there was one foot of water in the cottage-well, and two feet of water in the 
garden-well. In obtaining the temperature, the water was pumped till the reading 
of the thermometer remained constant. All the observations have been corrected 
for the scale error of the thermometer used. 
ACTINOMETER. 
94. The actinometer was made by STEVENSON of Edinburgh; it consists of a 
hollow cylinder of glass filled with ammonio-sulphate of copper. One extremity of 
the cylinder is joined to a thermometer tube, terminating in a hollow bulb; the 
other extremity is cemented to a metallic cap, through which a screw, working in a 
collar of leather, passes into the cylinder; a scale of 100 divisions is attached to 
the thermometer tube ; the cylinder and thermometer tube were inclosed in a maho- 
gany box, open at one side; the compartment containing the cylinder filled with 
the blue liquid is lined with black velvet, and is covered by a slip of plate- 
glass. The dimensions were as follow:—Glass cylinder, 54 inches long; mean 
external diameter, about 1-05 inch; the mercury, filling four inches of the thermo- 
meter tube, weighed 16-7 grains; the length of 100 divisions of the scale are equal 
