Sir James Jeans was a very competent mathematician who applied his talents mainly to the study of gases. However the nebular hypothesis has been revived by Weiszcker, with additional postulates which at least partially meet Jeans' criticisms. For some time Jeans had told his friends that at the age of 55 he proposed to abandon pure science and devote himself mainly to popularisation. In fact, as is so often the case, Jeans' idealistic account of probability is only a manifestation of mechanistic thinking. Labrenne is a professional mathematician, and his criticisms are based on a very considerable knowledge. In fact they go deeper than a reader might think at first sight. Lematre explains the reasons which made so many astronomers accept rather uncritically the arguments suggesting that planets were very rare. So that it was unlikely that there were intelligent beings on other stars.