Boston Elevated Railway jumbos. picture from annual report of the wire dept of Boston 1898. page 6 to 8 dicusses the laying of the cable for the elevated railway. Just before this picture the book says

"The constructions used for the support of the wires on the arched cross-girder of the structure is in effect, and it might be said, in fact, the same as. is in common practice on heavy pole line feeder construction, i.e., wood cross-arms, locust-pins, and petticoated glass insulators of the "Jumbo" type, the only difference being in the method of holding the cross-arms in place."