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7. To observe and record all Extraordinary Meteors, Lightnings, Thunders, Ignes fatuos, Comets, &c. marking still the places and times of their appearing, continuance, &c.
8. To carry with them good Scales and Glass-Viols of a pint or so, with very narow mouths, which are to be fill'd with Sea-water in different degrees of Latitude, and the weight of the Viol full of water taken exactly at every time, and recorded; marking withall the degrees of Latitude and Longitude of the Place, and the Day of the Month, and the Temperature of the Weather: And that as well of Water near the Top, as at a greater Depth.
The Viol is to be made with a very narrow Neck, and when it is almost full, water is to be dropt into it, drop by drop, till it can hold no more, drying well the Viol before it be weiged. The weight of the empty Viol is also to be recorded every time, weighing all to grains. And by evaporating gently the water, till the Salt be left dry on the bottom; they, who list, may have the satisfaction to know, what proportion the Salt of each water holdeth to its weight.
There is, among some other ways of finding the different gravities of Water, a very pretty one, mentioned by some Authors, as Johannes Toldenus (a German Artist) Cabæus, and Kircher in
his
