Translations for observation in French

Here are paragraphs from public domain books translated:

And seeing that the observation seemed to meet with approval, he enlarged upon his idea:	Et, la remarque paraissant juste, il insista :
The Confessions of Arsene Lupin, by Maurice Leblanc	Les Confidences d’Arsène Lupin, de Maurice Leblanc

"Perhaps Professor Summerlee may have an observation to make," he said, and the two savants ascended together into some rarefied scientific atmosphere, where the possibilities of a modification of the birth-rate were weighed against the decline of the food supply as a check in the struggle for existence.	— Le professeur Summerlee a peut-être, dit-il, quelque observation à faire ? Et les deux professeurs de partir pour ces irrespirables régions de la haute science où les conditions de la multiplication peuvent, en se modifiant, contrebalancer, dans la lutte pour la vie, la diminution de la nourriture.
The Lost World, by Arthur Conan Doyle	Le Monde perdu, de Arthur Conan Doyle