The white roadster on the right is the fabulous 1907 Thomas Model 35 Speedway Flyer. A true muscle car, their biggest engine in the smallest possible car. This is the model that ran and won the epic 1908 New York - Paris race. For more period images of this model see https://erthomasregistry.org/PeriodImagePages/35.html

There was a time when the comment boards would be filled with vehicular minutiae: I'll cover a year's subscription to the first person who can explain that marvelous contraption on the right.

[That hood says Packard to me. The color photo shows a 1916 Twin Six, minus the racing cowl of our Chicago car. - Dave]

Good catch! But ... Is there writing on the side "Silent Six"? Matheson had model by that name, and the roadster looks close.

[That’s a Packard hood. There are a zillion other roadsters from the era that "look close." - Dave]
An equitable ending(see top): we couldn't both be right, but... Not surprised the car ended up being notable as it seems as much the focus as the building.

I was born in Chicago in 1953. My family stretches way back in Chicago prior to the Great Fire of 1871. I could be looking at my relatives in these pictures and not even know it.