Answer:
The answer to your question would be that the conjunction in the sentence is "Not only... but also", a correlative conjunction.
Step-by-step explanation:
"Not only but also" is a correlative conjunction. What is important about the use of this construction is that the words following both parts of the it should belong to the same parts of speech. That is, if a verb follows not only, then a verb should also follow but also. In this case, a noun is placed after not only (Edison) and another noun is placed after but also (Bell). Consequently, it can be said the conjunction has been used correctly.