314 Royal Astronomical Society. 
easily, and honestly, it was found that the work was yet to begin ; 
that, in fact, the torsion pendulum was subject to every species of 
anomalous motion. In vain were such new precautions taken as 
these appearances suggested, and for eighteen months, a period so 
easy to speak of, so difficult to employ in activity under discourage- 
ment, no clue appeared to the solution of phenomena which seemed 
to set all the known laws of mechanics at defiance. Nothing could 
be more even than the temperature, even at the times when the 
anomalies were greatest; so that the effects of heat seemed to be 
out of the question as an explanation. The torsion rod, secure in 
a wooden case with thick glass ends, seemed to bid defiance to all 
external cause of currents of air; and so completely was the pen- 
dulum isolated, even from the case itself, that the latter might be 
violently shaken without any perceptible effect upon the former. 
Cavendish and Reich had both observed corresponding anomalies, 
but both apparently considered that their effects would disappear 
in the mean of a large number of observations. Mr. Baily resolved 
not to quit the subject until the cause of the anomalies was de- 
tected, and upon no account whatsoever to present a result vitiated 
either by assumption of the nature of the difficulty, or by rejection 
of the observations which appeared most discordant. To this 
resolute and honest determination we owe it that the paper for 
which this medal is given today is hardly less valuable as a lesson 
upon the nature and use of the torsion pendulum in measuring 
small forces than as a determination of the mean density of the 
earth. 
It was at last suggested, and, as I have before stated, by Pro- 
fessor Forbes, that possibly the radiation of heat from the large 
masses might, when they were brought up close to the torsion-box, 
or case of the pendulum, affect the inside of that case. It was 
already known that the evaporation of a few drops of spirits of wine 
sprinkled on the side of the case would produce a large and rapid 
effect on the pendulum. But between this frame and the large 
masses there had already been interposed a wooden screen, which, 
it was thought, would wholly prevent any effect of radiation. The 
suggestion above mentioned was accompanied by a recommendation 
that the outside of the case, and the masses themselves, should be 
gilt. Mr. Baily carried his precautions still further : the case was 
first wrapped in flannel over which a new case (gilt) was placed ; 
the masses, the plank which carried them, and the interior of the 
frame-work which inclosed both torsion-box and masses, were 
covered with gilt paper; the leaden balls at the two extremities of 
the torsion pendulum were gilt and burnished; and the masses 
were made to stand, when at the nearest, a little further from the 
torsion-box. These precautions proved to be sufficient ; the ano- 
malies were substantially removed, showing themselves only now 
and then, and in smaller quantities. The lesson thus read to ex- 
perimentalists on the effects of radiant heat will, it may be hoped, 
lead to further inquiries. Mere creation of difference of tempera- 
