Excerpt from Nova Acta Academiae Scientiarum Imperialis Petropolitanae, Vol. 6: Praecedit Historia Ejusdem Academiae Ad Annum 1788 Toute lunette armée d'un tel prisme achromatique, mefurera toujours avec beaucoup d'exaâitude tous les nu gles qui feront compris depuis zéro jusqu'à l'angle donné par la double réfraâion du cril'ral de roche: cet angle peut. Être de 40 minutes, il le cri¿al de roche ell taillé dela ma niere la plus avantageufe. On doit préférer le crill.1l de ro che de Madagascar à Celui d'eur0pe, pa'rcequ'il ell plus homo gène plus diaphane. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.