MACKIE — PHYSICAL ATsD C03MICAL PHE>^OMENA. 
181 
For this purpose, then, we commence in this article a series of 
speculations on possible phY^Jical and cosmical phenomena in refer- 
ence to the past conditions of our Earth, not always with the inten- 
tion of proposing new views or even our own opinions, but as often 
putting hypothetical cases to learn what would have been the results 
produced by particular conditions of physical forces and the exertion 
in particular directions of cosmical laws. 
At this lovely spring-time of the year, the briglit warm beams of 
the shining sun cause our eyes to rise to the blue and cloud-mottled 
sky. All around, the green buds are shooting forth, and flowers blos- 
soming and perfuming the bahny air. What would this beautiful 
world be witliout that sunshine? What would indefatigable, active 
man be without these cheering, life-exciting beams of the orb of day ? 
The sun is but a great fire ; lire, we know, consumes the substances 
it feeds upon; gigantic as the solar orb may be, the tire must burn 
it out, and, like the dark stars that astronomers now have indicated, 
the time may come when the earth, changed, perhaps, itself to a burn- 
ing mass, may reveal by its luminous beams to the astronomers of 
di4ant worlds its revolutions round an unseen, dark, extinguished 
sun. But without so deep a dive into the mysteries of time to come, 
let us ask ourselves what would be the eftect of minor alterations in 
the solar fire ? We cannot believe the solar flames are always burn- 
ing at exactly the same height, with exactly the same fierceness, 
giving exactly the same heat, exactly the same light. The fire on 
our hearth flickers, blazes, grows dull, requires fresh fuel, smoulders, 
bursts into flame again, burns clear and ruddy, glows with radiant 
heat, darkens, chinkles, and goes out. The consumption of the solar 
tire must be supplied; we cannot believe that as particle by particle 
is consumed, particle by particle is supplied. Even if meteors supply 
the sun, they must vary in abundance at diff'erent periods of time. 
If worlds fall in occasion;'.! ly to supply the waste, the solar fires at 
that spot must slacken, deaden, to glow out again briglit and more 
furiously M'hen the new fuel is ignited through. Eor geological pur- 
poses, without cooing into (jreat variations of the solar tire, let us con- 
ceive two moditications, — one of 15° nicrease of temperature from such 
a cause, and one of 15° decrease. We are told the centre of the 
earth is a burning incandescent fluid mass, — rather an uncomfortable 
idea, and not quite intelligible. We are taught it, liowever, mainly 
because the fossil relics of former creatures and plants are supiyosed 
to indicate tropical conditions in latitudes wheie now temperate con- 
ditions prevail. Unfortunately, however, in digging down into the 
bowels of the earth we do not find the temperature increase more 
and more with the depth, the heat increase faster and taster as we 
get nearer and nearer to this imaginary central melting-pot ; we do 
not, in short, find the heat of the handle increase more rapidly as we 
pass from the knob to the red-hot end of the poker. Just as Glaisher 
going up in the high regions of the air has disproved the old doc- 
trine of a supposed decrease of one degree of heat for every 300 feet 
of vertical height, jiud found a gradually diminishing scale of loss, 1° 
