Perturbations

Perturbations, name given to irregularities or slight deviations in the movement of a heavenly body, due chiefly to the neighbourhood of another point in its orbit.

Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)

Pertinax, Helvius * Peru
Persians
Persians, The
Persiflage
Persigny, Fialin, Duc de
Persius
Persius
Perth
Perth
Perthshire
Pertinax, Helvius
Perturbations
Peru
Perugia
Perugino
Peschiera
Peshawar
Peshito
Pessimism
Pestalozzi, Johann Heinrich
Pesth
Petalism