Do you know why Newlands' proposed the law of octaves?

Do you know why Newlands’ proposed the law of octaves ? Explain your answer in terms of the modern structure of the atom.

We know that the number of electrons in valence shell can vary between 1 to 8 but when inert gases were not known, it can range between 1 to 7 and hence next element must be similar to one of the first seven. So Newlands’ proposed the law of octaves.