Georg Simon Ohm was a German scientist who proved the relations between voltage, current and resistance. The resistance increase or decrease depends on the metal used for wires and for a same metal depends on his diameter and his lenght.
Please see the animation: the wire is a copper wire, the galvanometer marks a very little voltage and the lamp produces her normal light.
Almost all the current of the battery pass in the lamp.

Now the wire is a costantan wire (54% copper + 46% nickel) and his diameter is more little than the copper wire used before.
The lamp produces little light and the galvanometer marks more voltage than before.
The ohm's law tells that if voltage remains the same an increase of resistance decreases the current: