REPORT ON ASTRONOMY. 
139 
that upon using his Table the obliquities, from his own obser¬ 
vations, came out equal from the two solstices. He had re¬ 
marked {Berliner Jahrbuch, 1825, that Bradley’s observations 
gave equal obliquities, and in a paper in the Zeitschrift fiir 
Astronomie , vol. i., he endeavoured to show that the observa¬ 
tions of all the different observers make the obliquities equal. 
The difficulty depends (probably) on one of the nicest points 
about refraction, namely, the thermometrical correction. It is 
perhaps not easy to ascertain the exact temperature of the air 
at the time of the sun’s passage ; and perhaps the difference 
between the temperature within and without the transit-room 
(that stumbling block to astronomers and theorists,) may then 
be considerable. Perhaps also the colours on the sun’s limb, 
produced by atmospheric dispersion, may produce some doubt. 
On the whole, I conceive that this question cannot yet be re¬ 
garded as settled. The subject is well discussed in Caccia- 
tore’s Observations. 
In the Transactions of the Royal Irish Academy , vol. xii. 
for 1815, Dr. Brinkley published investigations on refraction, 
principally astronomical. In vol. xiii. he extended them to 
observations near the horizon: tables were formed from these 
materials. 
In the Phil. Trans. 182 3, Mr. Ivory published a theoretical 
investigation of refraction : it proceeded principally on the sup¬ 
position that, on ascending uniformly, the temperature of the 
air decreases uniformly: the result of this inquiry was given 
in tables. In the Phil. Trans. 1824, Dr. Young proposed a 
simple formula for the relation between the density and pres¬ 
sure of the air, which corresponded nearly to Mr. Ivory’s. 
The most remarkable, by far, of all the investigations of re¬ 
fraction that I have seen, is one by Mr. Atkinson in the Me¬ 
moirs of the Astronomical Society, vol. ii. To discover the 
law of the decrease of temperature, this gentleman collected a 
number of observations of the thermometer, made at various 
elevations by different persons ; and fixed at last upon this law T : 
That uniform decrements of temperature correspond to incre¬ 
ments of height which are in arithmetical progression. For 
the effect of temperature on the density of air, and for the 
whole refraction of air, the best experiments were referred to. 
The calculation was effected by a method of quadratures, 
the air being (for low refractions) supposed to be divided into 
sixty-four strata. The result is given in tables. It is to be 
regretted that the untimely death of the author prevented the 
completion of a second paper on nearly the same subject. 
Before quitting the subject of refraction I may point out two 
