46 
REPORT— 1847* 
of the preliminary observations from my paper entitled ‘ Researches in Phy¬ 
sical Geology,’ published in Part 11. of the Transactions of the Royal Society 
for 1839. 
“Ill the fii-st place, we may observe that there are two distinct processa 
of cooling, of which one belongs' to bodies which are either solid or imper¬ 
fectly fluid, and is termed cooling by coMittcliont and the other to nmajesin 
that state of more perfect fluidity which admits of a free motion of the com¬ 
ponent particles among themselves. In this ease the cooling is said to take 
place by circuhlion or convection. The nature of the former process bts 
been ascertained with considerable accuracy by experiment, and the laws of ihe 
phcBiiomena have boon made the subject of inatheiimtical investigation, but of 
the exact laws of cooling by the latter process w u are comparatively ignorant 
It is manifest, however, that since riV/n-’must be in'cessary for the transmission 
of the hotter and lighter particles from the central to the superficial parti of 
the mass, as well as for that, of the colder and heavier particles in the opposite 
direction, the temperaturu must increase with the ilejith beneath the sur¬ 
face; and, moreover, that this increase will be the more rapid, the mo« 
nearly the fluidity of the nia.ss npproacJjcs that limit at w Inch this proecw of 
cooling would cease, and that by conduction begin, since the rapidity of cir¬ 
culation would constaotly diiiiinish os the fluidity should ajiproximate to that 
limit. But still, even in this limiting case, it hctitiia probable that the ten¬ 
dency to produce an equality of temperature throughout the mass will be 
iniKui greater, and consequently the rate of increase of temperature in ap¬ 
proaching the centre uiiich less, tJmii if the cooling of the mass had proceeded 
by conduction during the saum time, the conductive power being very 
y circulation. Ihe iiianiier in which the transition will take place from 
I ^*^L*^*^^^^*''‘^*** by conduction, depends on certain con- 
with the di^ance from the surface while the 
denends on circulation, the tendency to solidification, so far as it 
but on the otlipr S^'catcRt at the surface and least at the centre; 
the centre" a ^ the pressure is least at the surface and greatest at 
cause, will ‘be greatest^ at'thc solidify, as depending on tba 
this tc’ndeiu.v n,w !! o ‘ “ • i ‘ at the surface. To estimate 
in the first ^ular.. /!“ °*‘■**^“*'he necessary, 
creases ?n d^ know the law according to which the temperature in- 
hy circulation - _ centre, while the ma-ss is cooling 
solidification as eoninarm*i\.^ti*.'n the temperature in resisting 
however, arc uoiiits mi n-i • of the pressure in promoting it. These, 
evidence, and^thereforo tlie"onr*^ posseas at prcserit little or no experimental 
that if the augmentation of ^ conclusion at which we can arrive is this,— 
rapid, that its effect in r« • »• '® with that of the depth be so 
‘»f^tlie iiicrc-fuie nfV? ® the tendency to solidify be greater than that 
•Jency t^rcol ^ greatest ten- 
ficiuh portions of tim m a»t aherwarda to solidify in the super- 
pressure S."Lntoorri; ^hc aigmentation of 
feet to imSet fluidir this transition from par- 
centre. ^ uubaoquent solidity, will commence at the 
” If wc suppose tlio former of these 
cases to hold, it 
W’ould appear that no 
