Clouds In Summer Or Harvent

In Summer or Harvest, when the Wind has been South two or

three Days, and it grows very hot, and you see Clouds rise with

great white Tops like Towers, as if one were upon the Top of

another, and joined together with black on the nether Side,

there will be Thunder and Rain suddenly.

WE may very easily account for this Observation, because in Fact the

Signs here mentioned ar
no other than Nature's apparatus for a Storm

of Thunder and Lightning, which will be perfectly understood by

attending a little to the Causes of these Meteors. Lightning is a great

flame, very bright, extending every way to a great distance, suddenly

darting upwards, there ending, so that it is only momentaneous. The

Matter which produces the Fire, is the Oil of Plants, attenuated by the

heat of the Day, and raised on high. Then whatever has exhaled from the

Earth that is sulphureous or Oily, which is dispersed up and down in

the Atmosphere, and is not continuous, is set on Fire by Turns, and the

Flame dilates itself as far as the Tract of that Exhalation reaches.

Some other Substance pendant and floating in the Air meets with this

also, with which it excites an effervescence, takes Fire and flashes

along with it. Thunder is another bright Flame, rising on a sudden,

moving with great Velocity through the Air, according to any

Determination upwards from the Earth horizontally, obliquely, downwards

in a right Line, or in several right Lines as it were in serpentine

Tracts joined at various Angles, and commonly ending with a loud Noise

or Rattling.

IT is observed that it thunders most when the Wind blows from the

South, and least when it blows from the East. The great Principle of

Thunder is Sulphur, as is evident from the Smell it leaves behind it;

but in order to occasion such an Explosion, there must be other

Ingredients mixed therewith, especially Nitre, of which the Air is

always full, besides other Things, of which it is impossible to give

any Account. The Tracts of this Sort of Matter fly about in the Air,

and are as it were Lines of Gunpowder, and as in the firing of that

Powder, the Fire begins at one End, and pursuing its Aliment proceeds

to the other Extremity, and so the whole Mass of Powder is fired; we

may from thence account for the Phaenomenon of Thunder. For in like

Manner those inflamed Tracts which are suspended in the Air, flash from

a Flame that runs from one Extreme to the other, wherever the Vein of

Nourishment leads it. Hence those Rays of Thunder, which seem to be

brandished through the Air, and sometimes to be split in two or more

Tracts, and sometimes to return back, at other Times to be projected in

Lines that are joined by various Angles, and this only because the

Flame meets with Tracts lying in various Situations that cohere one

with another. Therefore Thunder seems now to run horizontally, now from

above downwards, now upwards from the Earth, for if the Matter of

Thunder pressing out of the Earth is enflamed near the Ground, the

Flame darting upwards, the Thunder will seem to be projected out of the

Earth. If the same Tract be set on Fire at its upper end, the Flame

will move downwards, and the Thunder will seem to descend out of the


HENCE we easily understand how it comes to thunder oftener in one Place

than another, but most frequently in those where the Soil produces

odoriferous Herbs, and abounds with Sulphur, and where the People are

much exposed to the extreme Heat of the Sun. Thunder is less frequent

in Places where there are few odoriferous Herbs, very little Sulphur,

or where the Climate is watery and moist. For Instance, it thunders

very much in Italy and Sicily, and very rarely in Egypt, and the

adjacent Countries. If it be demanded how it comes to thunder in the

midst of the Ocean? The Answer is easy, because from the Bottom of the

Ocean vast Tracts of sulphureous Matter are cast up through the Waters;

as it happens to spring Waters in several Places, the Streams of which

will take Fire from a lighted Candle. For sulphureous Exhalations

bursting out together with the Waters, the fulmineous Matter in the Air

is set on Fire when it meets with Exhalations or Vapours with which it

can excite a vehement Effervescence. It is very clear from this

Account, that the Clouds mentioned at the Top of the twenty-eighth Page

are thunder Clouds, or Clouds big with the Materials of Thunder.