New-York tribune., 1878-07-22
nRLGLN nF HFAT HAYES.


ORIGIN OF HEAT WAVES.
Now that the torrid season is practically over, one
of the questions naturally suggested by the terrific
heat waves which spasmodicaly fall upon us Is;
What is their origini Are they due to local intiu-
ences or directly caused by fluctuations in the sun
itself Does that great source Of light and heat
remain uniform in its supplies It's forces sub
iect TO periodic ebb and flow In short, is the sun
a variable start Startling as affirmative an
swer to this last question might appear, there
would really bo nothing strange in such fact
The fixed stars are known TO be gigantic
suns, shining by their own light, and CIV
ing out, undoubtedly. enormous quantities
of heat, although we are too distant TO
perceive it, and each is probably the centre OF an at
tendant system of planets, just as our sun is Yet
among these far-of worlds we find many subject TO
periodic variations of brilancy appearing and dis
appearing with almost clockwork regularity, or sud-
denly flashing up as new stars and quickly fading
away forever.
One Of the most striking examples OF this varia-
bihty is the star Mira, Z" the wonderful" IN the
constellation of The Whale. This singular body
passes every year through a succession of changes
40 extreme that for five months il is absolutely in
visible. although, when at its brightest it equals
in splondor a star Of the second magnitude
Its greatest brillancy too. is not always the same
II does not increase OF diminish by the same grada
tons nor arc the successive intervals of its varia
lions constant In fact while the average period Of
its changes is abOut 331 days, the star is also sub
iect 10 many minor irregularities. Another variable
sun of short period is Algol in Perseus. At its
brightest tins star is commonly of the second mag
nitudc but in less than four hours IL falls 10 one Of
the fourth magnitude, aud remains IN that condi-
ton for twenty minutes. Then it begins to increase
IA brightness aud in three hours and half more
has regained It's rank as second magnitude star,
and continues TO hold It for two days aud hail.
when 1t again passes through its periodic changes
These are by no means isolated cases. The number
of stars known 20 be variable is large; Of them
pass through their round Of variations in long
and others in short periods, and all apparently
liable to fluctuations which conform to no fixed
rules.
Several facts seem TO indicate that our sun is r
variable star of the samo kind, though not subject
to such extreme changes Mira and Algol. It is
friahtful to think what would happen if it dsap-
pearcd altogether for four years, as Mira once did,
or even n it went through such rapid variations Of
brllaucy rs we see in Algol but that the does
vary can hardly be doubted. In some years its
face is found to be- almost perfectly mt rest. In
Others its forces TO be in extraordinary state
of activity, giving rise TO enormous spots which
undergo the most rapid and violent changes, and
throwing out vast masses of incandesoent gases TO
inconoeiynble distances. Bow these changes are
produced still remains mystery. On the supposi-
ton that the suns heat was kept mp by a constant
stream of meteors falling into that body II was
natural to suppose that the variations in the amount
of heat thrown OFF depended upon Irregularities in
the supply of IT'S metooric fuel On the more gener-
ally accepted theory, however that the temperature
a ab hv hO Of
meteors but by the contraction ofIts mass, these
variations of heat and light probably due to cor
responding variations in the process of condensation
Judging from the outbreak and disappearance of
solar spots it seems probable that the sun goes
through these changes. on an average. every eleven
wears though tho time may extend to thirteen years.
or be less than ten. Taking this period of eleven
years and remembering that Jupiter reyoyes
around the sun in nearly the same period, some as
tronomers have sought to show that the greater Of
the solar variations were due to the action of that
planet, while Others have argued that the minor
changes were caused by the earth and Venus. These
views however, seem TO rest OH no solid foundation.
But whatever be the cause, il may be safely
assumed from the periodic prevalence and disap-
pearance Of the spots and from other indications.
that tine SUM- like so many of the stars. is really
variable, passing through ts phases in a period
of about eleven years and that TO its yaria-
tions and not TO local Influences. must be ascribed
those extraordinary outbursts Of heat which
make life intolernbe in Summer and are doubtless
the origin Of our exceptionally mild Winters II
seems probable, too. that our heated terms are
likely TO be much in the years of
sunspot abundance. than in those when solar dis
turbances are few, though on this point there is no
conclusive evidence. The fearful heat of 1872,
however, occurred near the san-spot maximum,
while the milder inhictiOns both of this Summer and
of $40 happened near the sun-spot minimum. Fu-
ture observations will no doubt throw much light
on these obscure points, aud it may be that
our knowledge of solar physics increases shall be
able TO predict the arrival Of these unusual heat
waves. and thus rob them OF half their terrurs