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10. I think that the more circles are made at the 
fame time, the more delicate will the colours be; 
whereas the furface is, as it were, torn, or corroded by 
more violent explofions ; which makes the colours 
appear rough and courfe. N° 4. is I think on this 
account, as well as fome others, marked in a more 
delicate and beautiful manner than N° i.or N° 5. 
But this roughnefs is only perceived on the fteel. On 
filver, tin, and polifhed brafs, the colours were always 
free from that roughnefs. 
11. A polilhed furface is not necefiary, the colours 
being very manifeft on the rough fide of the fteel, 
where it is not covered with the black dull men- 
tioned above. 
12. Thefe coloured rings appear almoft equally 
well on all the metals on which I have made them ; 
namely, gold, filver, copper, brafs, iron, lead, and tin. 
I have not tried any of the femi- metals ; but I have 
no doubt of their anfwering as well as the proper 
metals. 
13. When the pointed wire was made to incline to 
the plane on which the colours were exhibited, the 
circular fpot was quite round, the center of it being 
in the perpendicular let fall from the point ; but the 
colours were projected oppolite to the point, in an 
oblong figure. 
Upon fhewing thefe coloured rings to Mr. Canton, 
I was agreeably furprifed to find, that he had, like- 
wife, produced all the prifmatic colours from all the 
metals, but by a different electrical procefs. His 
method had been to extend fine wires over the fur- 
face of pieces of glafs; and when the wire was ex- 
ploded, he obferved that the glafs remained tinged 
Vox. LV 1 II. L with 
