20 SEVENTH REPORT—1837, 
On Experiments relative to the influence of Surfaces on Radiation. 
By Proressor PowELt. 
The object of this communication was to call the attention of the 
Section to the researches of Professor Bache, of Pennsylvania, which 
seem not to have been so fully appreciated in this country as they 
deserve ; that gentleman, at the outset of his inquiries, refers to a 
paper of Professor Powell, in which the difficulties unavoidably attend- 
ing any comparison of radiating effects of surfaces are pointed out, 
from the impossibility of determining precisely in how many other 
respects, besides those of colour and polish of surface, the coatings 
applied may not differ. In contending for the necessity of equalizing 
the coatings compared in other respects, before we can estimate the 
effects really due to the surface, he must of course be understood to 
speak under the qualification acutely referred to by Professor Bache 
dependent on the fact first noticed by Leslie, that radiation takes 
place not only from the surface, but from a certain minute though 
sensible depth, which differs in different substances. Taking this 
into account, the general meaning as well as importance of the caution 
will be manifest. In the sequel Mr. Bache gives some very exact 
experimental proofs of the truth of the law just noticed, and shows, by 
successively adding fresh coats of the pigment, the precise limit beyond 
which such addition ceases to increase the radiating power; which, in 
fact, there comes to a maximum, and with greater thicknesses de- 
creases. When this point had been carefully ascertained in each 
pigment, their effects were observed with great accuracy, and compared 
with a standard surface under similar circumstances. The observa- 
tions include a considerable range of substances, differing both in 
colour and other properties. The results exhibit mo correspondence 
of the greatness of effect with the colour. 'The source of heat was hot 
water. The author allows fully the distinction between properties of 
heat of this kind, and that connected with light; in the latter case it 
is evident that colour is an essential element. A wide field is yet open 
for tracing on what the effect does depend ; and, again, since Melloni 
has pointed out the existence of many kinds of heating rays, to trace 
their several relations to surfaces. 
An Account of the Magnetical Observatory now in course of erection at 
Dublin. By Rev. Proressor Lioyp. 
In bringing this subject under the notice of the Section in its pre- 
sent stage, Mr. Lloyd said that he trusted little apology was required. 
The establishment of permanent magnetical stations had been urged by 
the powerful recommendation of the British Association; and he was 
sure that that body would view with interest the progress of an under- 
taking, which was sanctioned by its own authority. 
The magnetical observatory now in progress at Dublin is situated 
in an open space in the gardens of Trinity College, sufficiently re- 
