When analyzing a text, and trying to decide what information is relevant and which information is definitely not necessary to gather the main message of the writer, it is important to always first understand the purpose of the writer and then identify that information that, if it were taken away, would not damage the message being given. In this case, we are being asked about the details that allow us to understand the genius of Benjamin Franklin, and the passage gives us the information that he was considered a genius because he invented a harmonica that is made out of glass. Moreover, and more magnificent of all, is the description of how it works, because it gives the reader the image of how great, or not so great, the invention may be when compared to others. So, the first portion, "A glass harmonica was invented by Benjamin Franklin and is known as the Franklin harmonica" is necessary information because it allows the reader to know what the person is being mentioned for. The second part, the detailed description of the invention is also necessary. But the time during which the invention was used is not necessary information because it does not add or substract from the fact that the invention of this man was genius and that he, himself, was a genius. Therefore, the unnecessary detail is: "This instrument was popular in the 1800´s".
