ee 
Chemistry and Physics. A19 
was 3°°4 Cent. ey tbeniae two, which remained stationary. This 
that the tin vessels completely cut off the radiation, 
k,) and that the polished caps had the same effect. 
radiation of silver was determined by two ther- 
mometers cana with that metal—onena coyered, a oat in an 
d the: ird that of caeee ack. ‘The results of a series of. care- 
ful stecrvaMenie the radiating power of silver 3:026, that of lamp- 
black being 100.—being not far from the recent determination of MM. 
de la Provostaye and Dessains, by a quite different method. 
One eee precaution to be observed ‘in all tuna experiments 
is suggested by M. Melloni, we believe for the first time hou 
sahasteinont except at some distance from the ground and in dry 
weather—otherwise. the instruments soon become bedewed, and the 
high radiating power r of water soon brings them all:to the same degree, 
whatever be the nature of the c If the stems are left uncovered, 
the pecmometsrs are cooled down the bulb, and the same effect will 
be noticed. 
The radiating . power of the ialening substances was 9 obiginal by 
Pi, 2 them to the ¢aps of the thermometers. 
Lampblack, . . 10: Isinglass, : Repeat 
Carbonate of ee. ft, a tlass, 4 : eB 
Varnish, — ..9F  “Platnbago,. "sO 
The followi mparisoys were ma de by placing the substances i 
alittle heap one bottom of ‘the tin dish, and high enough just ic 
cover the cap of the thermometer. 
Lampblack, .° . ~~ . 100. Gaerdiat of poplar, . 99 
Smooth leaves from vari- “©  “pahogany, 95 
ous plants,  —_«. : Silicious ~ .: on 
Leaves of elm and poplar, 101. Mould, : . oe 
The portion of the sky concerned in the radiation is included within 
30° or 35° of the zenith. Even ints pape this a but little in- 
terfering effect. 
That radiation takes place not ult, from the sivkace but from the 
parts beneath, was proved me the greater radiation,of several coats of 
varnish than of a single on 
This explains a phaijementn which has been brought as an argument 
against Wells’ theory. It is objected that very thin bodies, such as spi- 
der webs, should recover their temperature from the air as fast as they 
lose it by radiation. Hence such substances should not be covered by 
the dew. But spider webs are notoriously productive of dew. M. Mel- 
loni contends that the piers) radiate from all portions of their ‘substance, 
and therefore lose much more than they can receive, in Peer ton to. 
br ‘bodies. 
A long continued course of experiment has satisfied M. Melloni, that 
the amount of sage is —_—? —— far teo high—that while under 
certain circumstance an be. cogled, to o 8° Cent. below the 
temperature of char air rane or five «iti general the effect of 
Re ae ee 
