Call derived class function from base class reference

Hello, is this possible?
I have a pure virtual function in the base class (to force the
programmers of the derived classes to have this function implemented)
but I want to call the derived class function from a base class
reference:

class A
{
public:
     virtual void function() = 0;
};

class B
:
public A
{
public:
     void function() { cout << "Hello" << endl; };
}

int main()
{
     B derived();
     A &base = dynamic_cast<A &>(B); // don't now if this is the way

     base.function(); // I need this type of call because I dont't
know the derived class type at runtime.
}

Of course I could have a function2 (private) and make it pure virtual,
and then have function() in base class calling the virtual function2:

class A
{
public:
     void function() { this->function_impl() };

protected:
     virtual void function_impl() = 0;
};

class B
:
public A
{
protected:
     void function_impl() { cout << "Hello" << endl; };
}

int main()
{
     B derived();
     A &base = dynamic_cast<A &>(B);

     A.function();
}

Is this good?
But... can I do it the first way?

Thanks.