[ 7 * ] ' 
upon the fteel, was made by a blunt wire, and N 5 2. 
upon the tin by a brads knob fixed oppofite to it. 
3. In making thefe rings, the fir ft appearance is a 
dulky red, about the edges of the circular fpot ; pre- 
fently after which (generally after four or five firokes) 
there appears a circular fpace > vifible only in a pofi- 
tion oblique to the light, and looking like a (hade on 
the metal. This fpace expands very little during the 
whole courfe of the explofions, and it feems to be, 
as it were, an attempt at the fir ft and fainteft red ; for 
by degrees, as the other colours fill the bulk of that 
fpace, the edges of this fihade deepen into a kind of 
brown 5 as may be feen particularly in N° 4. upon the 
fteel, where it is fomething more than half an inch 
in diameter, and in N° 1. where it is near i of an 
inch. 
4. After a few more explofions, a fecond circular 
fpace is marked out by another fihade, beyond the 
fir ft, generally about 4 or _L. of an inch in diameter, 
which I have never obferved to change its appear- 
ance, after ever fo many explofions. This fecond 
fihade, by fucceeding the firft; which as I obferved, 
becomes gradually of a brown, or a light red, feems 
to be an attempt at the fainter colours, which intervene 
between the reds. 
5. All the ftronger colours make their firft appear- 
ance at the edges of the circular fpot; and more explo- 
fions make them continually expand towards the ex- 
tremity of the fpace firft marked out, while others fuc- 
ceed in their place; till, after about thirty or forty ex- 
plofions, three diftind rings generally appear, as in 
N° 4. upon the fteel. If the explofions be continued 
farther, the circle becomes lefts beautiful, and lefs dif- 
tind 
