Query: What invention, for which he is primarily known, did Eli Whitney develop in New Haven?
Context: The city struck fortune in the late 18th century with the inventions and industrial activity of Eli Whitney, a Yale graduate who remained in New Haven to develop the cotton gin and establish a gun-manufacturing factory in the northern part of the city near the Hamden town line. That area is still known as Whitneyville, and the main road through both towns is known as Whitney Avenue.