SUN 
And hence arifes what is frequently obferved by tai- 
lors, viz. That when the Sun radiates obliquely upon 
the fea, as in the evening, there is no enduring his 
rays, by reafon they are all reflected from the water, 
and fcarce any loft therein ; fo that the re&itude or 
obliquitv of the rays contributes very confiderably to 
the collecting of fire. 
And this obliquity, &c. is to be confidered in a two- 
fold refpedt, both with refpect to the matter in the at- 
mofphere, and to the furface of the earth. 
Now heat may be varied two ways : 
1. By means of the atmofphere, for this does not 
always remain the fame. Thus, e. g. Water is natu- 
rally tranfparent, and if you warm it, it ftill retains 
its tranfparency •, but if you make it boil, the vapour 
iffuing from it, though perhaps a million of times 
rarer than the primitive water, will not be tranfparent, 
but opaque, by reafon its parts now are under a dif- 
ferent arrangement. 
And hence thofe legions of corpufcles every where 
floating in the vaft receptacle of the atmofphere, 
whenever they acquire a different difpofition, which 
they frequently do, alter the collection of the rays on 
the’earth. Add, that thofe white clouds, which ap- 
pear in fummer time, are as it were fo many mirrors, 
and occafion excefive heat. 
Thefe cloudy mirrors are fometimes round, fome- 
times concave, polygonous, &c. When the face of 
the heaven is covered with fuch white clouds, the Sun 
fiining among them mull of neceflity create a great 
heat, fince many of his rays, which would otherwife 
perhaps never touch our earth, are hereby reflected 
to us. Thus, if the Sun be on one fide, and the 
clouds on the oppofite one, they will be perfect burn- 
ing- glaffes. And hence the phenomena of thunder, 
&c. 
I have, fays Dr. Bcerhaave, obferved, a kind of hol- 
low clouds full of hail and fnow, during the continu- 
ance of which the heat was extreme, fince, by fuch 
condenfation, they were enabled to reflect much more 
ftrongly ; after this came a fharp cold, and then the 
clouds difcharged their hail in great quantity, to 
which facceeded a moderate warmth. Frozen, con- 
cave clouds therefore, by their great reflexions, pro- 
duce a vigorous heat, and the fame, when refolved, 
excefive cold. 
Hence it is probable, that thunder is only produced 
when fuch concave clouds, before convolved into 
fpherical figures, are driven with oppofite motions 
againft each other, and the rays tranfmitted through 
thofe fpheres from burning foci. 
All clouds, it is probable, contain fnow andice, but 
thefe in their fall through the warmer regions of the 
atmofphere near the earth, liquefy and diftil in drops. 
The meteors in the atmofphere have likewife their 
fhare in reflecting of fire. Thefe, in effect, are a 
fort of wandering fire vifible by night, and which de- 
termine the fire over and upon the earth. 
2. It is varied by means of the earth ; for, as the fur- 
face of the earth varies, fo muft the heat. Thus 
fandy places, reflecting more rays than others, muft 
excite a greater degree of heat. 
On the higheft mountains we always find the moft 
cold, fnow, and hail. 
In the iultry regions of Peru the mountains are all 
fummer long covered with fnow, by reafon they only 
receive direct, and but little refracted fire •, and the 
effedt of fire, arifing merely from being determined 
by the Sun into a parallelifm, is found by computation 
to be very inconfiderable. For this effedt, as already 
obferved, is greater in winter than in fummer. 
Though the Sun be in his apogee in the fummer, 
and in his perigee in winter, yet will a night’s ice 
bear it {tuning upon it five or fix hours ere it be 
thawed. 
And if, as the Sun rifes nearer toward the zenith, the 
ice and fnow at length begin to run, this is not owing 
to the greater force of the Sun, but to the greater re- 
flexion and collection of his rays from the circum- 
ftances and pofition of the atmofphere and earth. 
SUN 
But the higheft tops of hills are always free from 
fnow ; the reafon whereof is, that water, h e. the va- 
pours and exhalations, emitted therefrom, never rife 
by the Sun’s adtion above a mile high. But there are 
mountains a mile and a half high •, to the tops of thefe 
therefore, vapours, and confequently clouds, can ne- 
ver mount. 
And hence it is, that in very high mountains, as the 
Pico de Theide in Bohemia, though the middle part 
be eternally invefted with ice and fnow, and the bot- 
tom fcorched with intolerable heat, yet on the top 
you find yourfelf in a pure, thin, ferene air, and view 
the clouds hovering at a confiderable diftance below 
you. Hence alfo it is, that all thunder is confined 
within lefs than a mile’s height. 
Add, that in caverns, and the hollow parts under 
ground, the heat is found very great, fo that the air 
is coldeft in the higheft: places, and hotteft in the low- 
eft, but in the intermediate atmofphere very unequal. 
Heat therefore depends on clouds, mountains, &c. 
which reflect the light varioufly, and on the direction 
of the Sun’s rays, or the pofition of his body with 
refpect to us. 
Hence again we gather that fire is the univerfal 
caufe of all the motions about our earth, for all flui- 
dity depends on fire, and accordingly, -in the large 
burning-glaffes, the firmed: bodies become fluid, and 
evaporate in fume ; and the more fluid any body is, 
the more it contains, whence it is, that water, de- 
prived of all its fire, fixes into ice, and when ex- 
pofed afrefh to the fire refolves into water ; and aji 
fluids whatever, if deftitute of fire, would do the 
fame. 
The Sun may be accounted the parens nature, or 
the primum mobile of all vegetative motion. 
The Sun’s attractive virtue is very confpicuous in 
the exhalation of thofe crude and unwholelome va- 
pours, with which the earth is often infefted, which, 
if they were fuffered to continue long upon the face 
of the earth, would render it a miferable defart. 
The Sun, by fublimating thofe crude and hurtful va- 
pours, and their being rarefied before their defcenfion 
and diftribution, forms them into rain, which is of 
great conlequence in vegetation.' 
To this may be added the attraction of plants them- 
felves, which creates a kind of emulation in them, 
which fhall grow the talleft. 
But that which the ancients ufed to attribute to at- 
traction, may now be very well folved by pulfion. 
To apply which to the matter in hand : when the 
furface of the fea, &c. is divided by the heat of the 
Sun, and the power of the air, their afcenfion thro’ 
the atmofphere, either by the rarefaction of the air 
by the Sun, or otherwife by the refpiration of the ter- 
raqueous globe, which in this cafe may be fuppofed 
to aft like the body natural ; or elfe, that the air, 
being rarefied by the Sun beams, does, by the gra- 
vitation of his own body in general, force thofe hu- 
mid vapours by pulfion upward, through thofe beams 
or rays of light, which are, as it were, fo many pipes 
or tubes for their ready paffage, afcenfion, and con- 
veyance. 
Or if thofe vapours are conveyed by the undulation of 
the air in a perpendicular manner, rather than a ra- 
diant one, through the rays and beams of light, 
which foever of thefe ways it is, the Sun is the princi- 
pal agent in this bufinefs, and the whole procefs is ei- 
ther attraction, pulfion, or refpiration, forwarded by 
the virtual power of it. 
That the rarefaction of the air by heat is a great help 
to attraction or pulfion may be difeovered by the fire 
engine made by Mr. Savary. We cannot fay that the 
water is either forced or attracted by the heat, but 
that the air that is in the pipe is lengthened by its rare- 
fying quality to fuch a degree, that the equilibrium 
is loft, and the impulfe and prefftire of the air which 
is without, forces the water to that great height that 
is feen in the operation. 
And fo, if a little lcrip of paper burning and fuming 
be put into a common drinking glafs, and, it be turn- 
ed 
I 
