Footprints Without Feet: Footprints without Feet

What is the name of the invisible scientist in the chapter 'Footprints without Feet'?...

Where did the two boys follow the muddy footprints?...

Why did Griffin set fire to the house of his landlord?...

What was the condition of Griffin's clothes when he walked without them?...

In which store in London did Griffin take shelter for warmth and food?...