ON RADIANT HEAT. 
353 
eight years ; which would occasion an increase of 1" apparent diameter in 
40,000 years; a change of course utterly inappreciable to observation. 
The amount of matter thus abstracted by the sun would be equal to the 
mass of the earth in about forty-seven years; but it is quite conceivable that 
a quantity of 100 times this amount would not be missed from the zodiacal 
light. Thus the sun’s heat might be kept up for 5000 years to come at least. 
I his transfer of matter to the sun coming from a source within the earth’s 
orbits, would not affect (he conditions of the system, as to the effects of gra- 
vitation. ° 
Some meteors may possibly come direct on the sun from the extra-planet¬ 
ary spaces, but the quantity of such is probably very small in comparison 
with those that have been revolving in approximately circular or elliptic 
orbits before falling in. 
If we imagine a dark body moving through space and coming into a lo- 
rahty abounding with meteors, their impact may raise it to incandescence, 
which will cease when it moves out of that space. Thus the author suggests 
a possible explanation of variable stars. 
(Addition I.) The author gives a calculation of the quantity of matter 
necessary to be added Jo the sun, on the extra-planetary hypothesis, and finds 
u gives too great an increase of central force to consist with the historical 
wnd'tioDs °f the earth’s motion. He concludes the supply must have been 
rmiwthm the earths orbit for thousands of years at least 
(Addition II.) He shows that the resistance must be very small even close 
uicsun, since such light bodies as comets pass through it at perihelion, 
hvli'i a I tmo T I,crc may be conceived to be carried round in a vortex 
K T**’ b , Ut nut moK «!*% a planet n«ulU be at 
rplL® J 9 D ,ance * Hence the meteors must long continue to revolve before 
tty fJun SUn ’ an,t mwsl 80 nmr as 10 1)6 completely evaporated before 
h fc, f'f 11 ', ■ hmt }\ P ro(lHCeil > not by solids impinging on the sun , but 
(\,\ Tr t tl l0n °f ltw T0tatm 9 V( >rtex of evaporated meteoric mailer. 
mav Ta '•* Th .° tem P Gmturc of tlle different parts of the sun’s surface 
revolt™ 8 re at changes from the eddies and streams occurring in this 
streak | raas8, Hence man y of the appearances of the solar spots and 
oration'a Vi" IV *V‘ ? n the age ° f the Bun ” At rate meteoric 
incor- 
POratl ir 1 / v- true auu* LUC, 
iVomrest in°«ionon UlatCtJ ’ ^present istation of the sun would be produced 
that the J n ycars ’ We ma r ,nfer ( Bince it; appears very improbable 
that the kind a contrary rotation destroyed by meteoric incorporation) 
generating Lit Iv "° W g °" lg °’V canm>t have been going on and alone 
future up u a !'?, presenl ?' te > fo, ‘ more than that period. Vat the 
with that of m ‘ r nmSS ° f tbe 20(,iacal b ght is small, in comparison 
planets and «. * e BU °l lom V* P r °ducing no sensible perturbation on the 
The sun’s rlV may i C ? rC lt , cannot ke ^P up the supply for 300,000 years, 
possibly vf.ru * l0H mS becn , b y 110 means accurately determined; it may 
test the theory 0 30 amoun * wb ’ cb future observations may detect, and thus 
8 4ecUf r Sr ati0 !! # ? ,OScly connected with the former and the general 
density uhipi. has . een . P ur8U «d by the Bame author, on the probable 
, p ^ n u ^signed to the luminiferous and caloriferous aether. 
Tr ansactionTof'L Rn°, m i c" *. 0n ,? osslMe Densi, y of the Luminiferous Medium,’ &c., 
1854 . wtheRo yd Society of Edinburgh, v«l.xii. p ar tl. 
o 
Density of JEth er. 
2 A 
