228 M E M O I R S c/ the 
to be win-ied, that our honourable and learned judges would 
take this matter into their confidcration, whenever any bufincfs 
of this nature comes before them. 
^he Cavfe of Hail, Lightning, ^;;i Thundery hy Z>A Wallis- 
Phil. Tran{:^N° 251. p. (J53. 
THunder and lightning are fo very like tho Q?i^^^ of fired 
gun-powder, that we may realbnably judge them to 
proceed from like caufes. Now the principal ingredients in 
gun-powder are nitre and fulphur, the admixture of charcoal 
being chiefly defigned to keep the parts feparate, for the better 
kindling of it ^ fo that if wc fuppofe in the air a convenient 
mixture of nitrous and fulphureous vapours, and thofe by 
accident to take fire, fuch explofion may well cnfue, as in 
the firing of gun-powder^ and being once kiifdled, it will run 
on from place to place, as the vapour leads it, as in a train of 
gun-powder. This explofion if high in the air, and far from 
us, will either do no mifchief, or none very confiderable, like 
a parcel of gun-powder fired in the open air 5 but if it happen 
to be near us, or amongfl us, it may kill men or cattle, tear 
trees, fire gun-powder, break houfes, or the like, as gun- 
powder would do in the like circumflances. Now this diftance 
fnay be eftimatcd by the interval of time between feeing the 
flafli ot lightning, and hearing the noife of the thundery for 
tho', in their generation, they maybe fimultaneous, yet light 
moving fafter than lound, they come to us fucceffively. 
Dr. /r<^///i obfervcd that, commonly, the peal is about feven 
or eight ieconds after the flafli, that is, about half a quarter of 
a minute; but fometimcs, it is much fooner, as in a iecond or 
two, or lefs than fo, and almoll immediately upon the flafhj 
and at fuch times, the explofion mult needs be very near us, 
or even amongft us; and in luch cafes, Dr.Wallls has more 
than once prcfaged the mifchievous conlequences, which 
accordingly happened. Now that there is in lightning a ful- 
phureous vapour is manitcft from the fulphureous fmell which 
accompanies it, efpccially when any mifchief is done by 
It, and even when there is none, from the lightning itfelf, 
which is more or Icfs dif erniblc ; and a lultry heat in the air is 
commonly a forerunner of lightning, which is loon after to enluc 5 
and that there is alfo a nitroijs vapour therein, we may 
reafonably judge, becaufe wo know of no other body io capa- 
ble of a violent and fudden explofion as nitre. Now as to the 
kindling of thcfe materials, in order to fuch explofion, Chemifls 
obkrve that a mixture of iulphur, filings of fleel, and a little 
water. 
