T H U 
Dr. Wallis in Philof. Tranfact. N° 23 i; fays, That 
-Thunder and lightning are fo very like the eftefts of 
fired gunpowder, that we may reafonably judge they 
proceed from the like caufe. 
Now the prinipal ingredient^ in gunpowder are nitre 
and fulphur (the admiffion of charcoal being chiefly 
to keep their parts feparate, for the better kindling of 
it ;) fo that if we fuppofe in the air a convenient 
mixture of nitrous and fulphureous vapours, and thofe 
by accident to take fire, inch explofion may well fol- 
low with noife and light, as in the firing of gun- 
powder ; and being once kindled, it will run from 
place to place, as the vapour leads it, like as in a 
train of gunpowder, with the like effects. 
This explofion, if high in the air, and far from us, 
will do no mifchief, or not confi derable, like a parcel 
of gunpowder fired in the open air, where nothing is 
near enough to be hurt by it ; but if the explofion be 
near to us, or amongft us, it may kill men or cattle, 
tear trees, fire gunpowder, break houfes, or the like, 
which gunpowder would do in the like circumftances. 
This nearnefs or farnefs may be eftimated by the dif- 
tance of the time between feeing the flafh of lightning, 
and hearing the clap of Thunder; for though in their 
generation they be fimultaneous, yet light moving 
falter than found, they come to us fucceffively. 
I have obferved, that commonly the noife is about fe- 
ven or eight feconds after the flafh, but fometimes it 
is much fooner, in a fecond or two, or lefs than that, 
juft after the flaffi; and then the explofion muft needs 
be very near us, and even amongft us, and in fuch 
cafes, I have more than once prefaged the expefta- 
tion of mifchief, and it hath proved accordingly. 
The noife of Thunder is more diverfified in cloudy 
weather, becaufe the air is varioufly reverberated from 
the clouds to us ; but if there are no clouds, the air 
flows through the open fpaces to our ears, more freely 
and evenly, and it frequently lightens in fuch weather 
without Thunder, becaule the inflammation confifts 
only of fulphureous particles, and on the contrary it 
often thunders in cloudy weather without any light- 
ning appearing vifibly, becaufe it is intercepted by 
the clouds. 
Rain generally attends Thunder and lightning, either 
at the fame time, orfoon after, and it frequently rains 
fafter after a clap of Thunder, fo that rain feems to 
be the effecft of Thunder. 
As for Thunderbolts; when it thunder and lightens, 
there fometimes falls a Thunderbolt. This Thunder- 
bolt is a moft rapid flame, that darts out of the clouds 
to the ground, and ftrikes every thing that is in its 
way, and it is obferved to have the following peculiar 
phtenomena : 
1. That it oftener ftrikes upon high places than low, 
as upon mountains, towers, fteeples, trees, &c. 
2. That it fometimes burns peoples clothes without 
hurting their bodies. 
3. That it fometimes breaks their bones, and at the 
fame time does not hurt their flefh or their garments. 
4. That it has melted or broken a fword in a fcabbard 
without hurting the fcabbard ; and, on the contrary, 
has fometimes burnt the fcabbard all over, and at the 
fame time done no harm to the fword. 
From thefe confiderations we may conclude that a 
Thunderbolt is an exhalation kindled on a fudden, 
and is copious enough to be hurried down to us by 
winds. 
Thunderbolts are moft commonly darted aflope 
through the air, and this may be occafioned by the 
winds, which feldorn or never blow downright. And 
it is probable, that the flame is beaten down by the 
wind, and reaches the ground before the matter of it 
is quite fpent. 
And this may be the reafon that for the moft part 
they ftrike upon high places ; for, as they fall ob- 
liquely through the air, they often in their way meet 
with mountains, towers, &c. and the reafon that the 
force of their flame iswery different, is probably from 
the difference of the exhalations which form the 
Thunderbolts, the bodies from which they are col- 
T H U 
letted being fulphureous, bituminous, or faiine, and 
from thence it may be, that it fometimes burns gar- 
ments, at the fame time that it paries over the bodies 
without doing them any harm. 
Sometimes it penetrates the foftflefb. harrnlefsly, and 
yet breaks the hard bones, as gold and other metals 
are diffolved by aqua-regia and. aqua-fords, and in the 
mean time the paper fhall not be hurt by them : and 
for the fame reafon it is, that a fword may be melted 
in a fcabbard, and yet the fcabbard remain entire 5 
and fo it would be if they were both laid together in 
aqua-fortis, becaufe the acute parts of the aqua-fortis 
do not operate upon the foft matter, the particles of 
which are branched, as they do upon harder bodies, 
into the pores of which they infinuate themfelves, and 
diffolve the contexture. 
The effects of lightning upon vegetables are fome- 
times very great ; it fplits down trees, and there has 
been many inftances where the bodies of large trees 
have been torn to pieces, and the chips fcattered to a 
great diftance, but inftances of this are pretty rare. 
The killing of branches or parts of trees is very com- 
mon and fudden ; for when this happens, that part of 
the tree where the lightning ftrikes, will in a very few 
hours appear as dead as if it had been fome days fe- 
vered from the trees. 
THURIFEROUS fignifies bearing of producing 
frankincenfe. 
THUYA. Tourn. Inft. R. H. 586. tab. 358. Lin. 
Gen. Plant. 957. [fo called of to perfume with 
fmoke, becaufe this plant hath a penetrating fmeil.] 
The Arbor Vitas, vulgo ; in French, Arbre de Vie. 
The Characters are, 
It has male and female flowers in the fame plant ; the 
male flowers are produced in an oval katkin. The flowers 
are placed oppofite upon the common foot-ftalk , each flower 
embracing it with its bafe ; thefe come out of an oval con- 
cave fcale ; they have no petals , but have four ftamind 
which are fcarce difcernible ; their fummits adhere to the 
bafe of the fcale of the empalement. 'The female flowers 
are collected in a common almofi oval cone , two flowers 
ftanding oppofite in each fcale ; they have no petals , but 
have a fmall germen , fupporting a fender ftyle , crowned 
by a fingle ftigma ; thefe are fucceeded by an oblong oval 
cone , opening longitudinally , whofe fcales are almofi equals 
convex on the outfide , and obtufe , each containing an oblong 
feed with a membranaceoits wing. 
This genus of plants is ranged in the ninkh feftion. 
of Linnseus’s twenty-firft clals, which corftains thofe 
plants which have male and female flowers on the 
fame plant, and their ftamina are ctillefted in one body. 
The Species are, 
1. Thuya ( Occident alis ) ftrobilis laevibus, fquamis ob- 
tufis. Hort. Cliff. 449. Thuya with fmooth cones and ob- 
tufe fcales. Thuya Theophraili. C. B. P. 488. The 
common Arbor Vita. 
2. Thuya [Orient alls') ftrobilis fquarrofis, fquamis acu- 
minatis reflexis. Hort. Upfal. 289. Thuya with rugged 
cones , and acute-pointed reflexed fcales. Thuya ftrobilis 
uncinatis, fquamis reflexo-acuminatis. Flor. Leyd. 
Prod. 87. The China Arbor Vita. 
The firft fort grows naturally in Canada, Siberia, and 
other northern countries, but has been long an inha- 
bitant in the Englifh gardens. In fome of thefe gar- 
dens, which have ftot been altered, there are fome of 
thefe trees which are of a large fize : it has a ftrong 
woody trunk, which rifes to the height of forty feet or 
more. The bark, while young, is fmooth, and of a dark 
brown colour, but, as the trees advance, the bark' be- 
comes cracked and lefs fmooth. The branches are 
produced irregularly on every fide, ftanding almofi ho- 
rizontal, and the young [lender fnoots frequently hang 
downward ; thefe branches ftand but thin, and the 
younger branches only are garniHied with leaves, fo 
that when the trees are grown large, they make but 
an indifferent appearance, being fo thinly clothed with 
leaves. The young branches are flat, and the fmall 
leaves are placed imbricatim over each other like the 
fcale of fifli ; the flowers are produced from the fide of 
the young branches, pretty near to the foot-ftalk ; the 
13 F male 
