So it is a mystery to me why the two related puzzles that follow can't be found anywhere. This should correct that oversight. The rules are the same as for Dudeney's original. A move consists of sliding a coin from its current position into a new position into which it fits snugly, i.e., it touches two other coins, which fix its position.
I was lax in my definition of "fits snugly", for which I apologize. If three coins are in a line, none of them fits snugly in its position. Mathematically, the middle coin's position is defined exactly by the positions of the two end coins because there is only one spot at which the middle coin is tangent to both end coins. However, I was going for gut feeling snugness, not mathematical snugness. So, to clarify, coin A fits snugly against coins B and C if the A touches both B and C and the centers of the coins are not colinear.