■ . t 7° ] 
i . When a pointed piece of metal is fixed oppofite 
to a plain furface, the nearer it is placed to the fur- 
face, the fooner do the colours appear, the clofer do 
the rings fucceed one another, and the lefs fpace they 
occupy ; as, on the other hand, the farther it is placed 
from the furface, the later do the colours appear ; 
but the rings then occupy a proportionably greater 
fpace, and have more room to expand themfelves. 
N° i . on the feel % was made by the explofions pair- 
ing from the point of a needle, fixed at the diftance 
of _ 5 . of an inch from the fteel ; and N° 2. was made 
la 
at the fame time, when the needle was placed at the 
diftance of- 1 of an inch. It leems, however, that 
when the point is placed at fuch a diftance, as that 
the eledric matter has room to dilate, and form as 
large a circular fpot as the battery will admit, the 
rings are as large as they are capable of being made; 
but that ftill the colours appear later, in proportion 
to the diftance beyond that. When the point is 
fixed exceeding near, or is made to touch the fur- 
face, the colours appear at the very firft explofion, 
but they fpread irregularly, and make not diftind 
rings, as N° 1. upon the tin. 
2. The more acutely pointed is the wire, or needle, 
from which the eledric matter ilfues, or at which it 
enters, the greater number of rings appear. . A blunt 
point makes the rings larger, but fewer; and in that 
circumftance it is likewife much later before the co- 
lours make their appearance at a given diftance. N° 3. 
* All the coloured rings mentioned in this paper were (hewn 
to the Royal Society, but could not be well reprefented by a 
print. 
upon 
