Need help reading early 20th century stock market list
I am unfamiliar with this style of notation, but in my opinion it seems likely that the double fractions denote buy and sell prices. I.e. on Nov 29th 1911 the sell price was 104 3/8 and the buy price was 104 7/8. This gets you an average or mid price of 104 1/2 = 104.5.

It is also possible that the two numbers denote the daily opening and closing prices, but the variation seems small for this.