When Albert first meets Henry, he lays all the documents he brought on the table next to his host. When soon thereafter he turns around and sees Henry asleep, there is nothing lying next to him.
When Professor Wilmarth is waiting for young Mr. Akeley at the Boston train station, Wilmarth turns his head to see that the train is approaching. Although the image is out of focus, it is clearly a modern train, not one that would be seen in the 1920's.