The side-view photo is on "Pinterest" (I found it by searching "Macpherson motor car) with the blurb
"MacPherson gasoline motor baggage car used on the Pennsylvania Railroad on March 28, 1914"
and something about "Steven Allen's" favourite PRR photos. ????
At a guess, then, Macpherson was an inventor/developer/manufacturer, whose claim that his 4-4-0 rail motor would provide, as Train Detainer says, a way of reducing branch line costs was plausible enough that the PRR invited the demonstrator for a demonstration visit. (And, since we haven't heard anything about it otherwise, sent it right back: there were, I suspect, many unsuccessful efforts at designing rail motor cars. By 1914, GE had a usable design of gas-electric on the market: I don't know if PRR bought any of theirs, but they would have known about them, and wouldn't have bought something that seemed inferior to them. I can't tell from the photo exactly what sort of transmission the car had, but at a guess it was straight mechanical, and mechanical transmissions for gasoline-engined rail vehicles don't have a happy history.)