On both of these cards, you see the pantographs above the streetcars; that's the electric rod device that collects electric current from the overhead lines. You don't see the overhead lines themselves though. They would have been visible on the photograph, but were often erased when the photo was colorized. Sometimes the pantographs weer also erased. It made for a cleaner picture.
Line 4 below, also replaced a horse-drawn service, and was added in 1906.
meubilair, which is the word for furniture in Dutch.
Here are the backs of the cards in the same order.
The message, sent in 1908, reads
Our sincere greetings from the second house on the left. Your devoted E.M. Pool
For a complete history of trams in Rotterdam, visit The Tram of Rotterdam website.