Thank you to my fourth cousin (descended from the sister of Esther Abigail Whitman) who found my blog and shared the following with me.
and on the back:
Without extensive research, I'm theorizing that "Grandpa Bruce" is William Wallace Bruce (1863 - 1906), and the first cousin of James Tolman Pyle (1855 - 1912), which makes sense as this looks like the photo of a young man (see a photo of my grandfather for a family resemblance) perhaps in his 20's, so taken around 1880. (I'll take advice on dating of the photo in the comments below.)
In checking a few New York City directories on Fold3, I find that Frank or Francis P. Macnabb was a New York City photographer from about 1875 until after 1900. He was at 815 Broadway from 1875-1883, which helps in dating this photo. His address changed to 813 Broadway in 1884.
I never knew that my great grandfather was called "Jim."