visible effects upon the rays of Light, without any other coefficient cause: and then, that there is in the Air or Atmosphere, such a variety in the constituent parts of it, both as to their density and rarity, and as to their divers mutations and positions one to another.
He concludeth with two Celestial Observations; whereof the one imports, what multitudes of Stars are discoverable by the Telescope, and the variety of their magnitudes: intimating with all, that the longer the Glasses are, and the bigger apertures they will indure, the more fit they are for these discoveries: the other affords a description of a Vale in the Moon, compared with that of Hevelius and Ricciolo; where the Reader will find several curious and pleasant Annotations, about the Pits of the Moon, and the Hills and Coverings of the same; as also about the variations in the Moon, and its gravitating principle, together with the use, that may be made of this Instance of a gravity in the Moon.
As to the Inventions of Art, described in this Book, the curious Reader will there find these following:
1. A Baroscope, or an Instrument to shew all the Minute Variations in the Pressure of the Air; by which he affirms, that he finds, that before and during the time of rainy weather, the Pressure of the Air is less; and in dry weather, but especially when an Easterly Wind (which having past over vast Tracts of Land, is heavy with earthy particles) blows, it is much more, though these changes be varied according to very odd Laws.
2. A Hygroscope, or an Instrument, whereby the Watery steams, volatile in the Air, are discerned, which the Nose it self is not able to find. Which is by him fully described in the Observation touching the Beard of a wild Oate, by the means whereof this Instrument is contrived.
3. An Instrument for graduating Thermometers, to make them Standards of Heat and Cold.
4. A New Engine for Grinding Optick Glasses, by means of which he hopes, that any Spherical Glasses, of what length