Pamphlet with pink, untitled cover. A calculation of the average density of the earth following observations by George Biddell Airy by Royal Academy, Belgium, correspondent, François Folie. A reprinted extract from the Academy's bulletin including Folie's calculations and reasonings. 5th May 1872. Printed in 1878 by F.Hayez, Brussels. Sur le calcul de la densité moyenne de la terre, d'aprés les observations d'Airy
