Some activists for civil rights registered their feeling by means of protest. what is the object of preposition by means of

There are 3 prepositional phrases: for civil rights, by means, and of protest. As a general rule the object of the preposition follows the preposition and is always a noun. So in the phrase for civil rights the object would be rights (civil is an adjective describing rights). The object of "by means" is means. The object of "of protest"