Tho’ some of the properties of steam are well known; yet the degrees of expansion it is capable of; whether air be mixed with, or necessary to, its formation; as also how far its power of resistance may reach; are probably not yet known, to a proper degree of exactness. Niewentit fixes the expansion of a cubical inch of water, converted into steam, at 13365, Dr. Desaguliers at 14000, and Mr. Payne at 4000 times. The great scope in this subject from a plenum to a vacuum, if I may be allowed the expression, as also the very useful purposes, to which it has already been, and possibly may be still further applied, will, I hope, be an inducement to those, who are much better qualified, to proceed in so useful an inquiry. XLVI. _Observatio Eclipsis Lunæ Die 27_ Martii, _Ann. 1755. habita Ulissipone in Domo Patrum Congregationis Oratorii à_ Joanne Chevalier _ejusdem Congregationis Presbytero, Regiæ_ Londinensis _Societatis Socio, Regiæque_ Parisiensis _Scientiarum Academiæ correspondente_. Tubo optico 8 pedum peracta est observatio cœlo sereno, claroque. [Read Dec. 8, 1757.] IMMERSIONES. Hora postmeridiana temporis veri. h ’ ” Initium penumb rædubium 10 29 50 Initium eclipsis dubium 10 33 35 Certe jam incæperat 10 34 05 Umbra ad mare humorum 10 44 00 Umbra ad Grimaldum 10 44 53 Grimaldus totus in umbra 10 47 58 Mare humorum totum in umbra 10 51 14 Thico incipit mergi 10 53 29 Thico totus mergitur 10 55 14 Umbra ad Reinholdum 11 08 04 Umbram ingreditur Copernicus 11 19 22 Umbra ad mare nectaris 11 24 52 Totum in umbra 11 33 50 Umbra ad mare tranquillitatis 11 35 24 Promontorium acutum in umbra 11 45 46 EMERSIONES. h ’ ” Incipit emergere ab umbra Copernicus 12 04 38 Totus Copernicus extra umbram 12 07 40 Incipit egredi Grimaldus 12 09 38 Totus Grimaldus extra umbram 12 12 38 Incipit emergere mare fœcunditatis 12 31 37 Emergit mare humorum 12 36 11 Incipit emergere Capuanus 12 39 40 Egreditur Schicardus 12 48 30 Emergit Thico 12 51 40 Totum mare nectaris egreditur 12 58 09 Finis eclipsis 13 13 02 Finis penumbræ dubius 13 16 50