_March_ the 29th, the Thermoscope in the Air was at 8-7/8 inches; being put into a somewhat large evaporating glass, fill'd with water, it fell (after it staid a pretty while, and had been agitated in the liquor) to 8. inches: then about half the Salt, or less, that had been used _twice_ before, and felt much less cold than the water, being put in and stirr'd about, the tincted Spirit subsided with a visible progress, till it was faln manifestly beneath 4. inches; and then, having caused some water to be freshly pump'd and brought in; though the newly mention'd Solution were mixt with it, yet it presently made the Spirit of Wine manifestly to ascend in the Instrument, much faster, than one would have expected, &c. And this much may suffice for this time concerning our _Frigorifick_ Experiment; which I scarce doubt but the _Cartesians_ will lay hold on as very favourable to some of their Tenents; which you will easily believe, it is _not_ to the Opinion, I have elsewhere oppos'd, of those Modern Philosophers, that would have _Salt-petre_ to be the _Primum Frigidum_: (though I found by trial, that, whilst 'tis actually dissolving, it gives a much considerabler degree of Cold, than otherwise.) But about the Reflexions, that may be made on this Experiment, and the Variations, and Improvements & Uses of it, though I have divers things lying by me; yet, since you have seen several of them already, and may command a sight of the rest, I shall forbear the mention of them here, not thinking it proper, to swell the bulk of this Letter with them. * * * * * _An Account of two Books lately printed in London._ I. _EUCLIDIS ELEMENTA GEOMETRICA, novo ordine ac methodo demonstrata._ In this compendious and pretty Edition, the Anonymous Author pretends to have rendred these Elements more expeditious; by bringing all together into one place, what belongs to one and the same subject: Comprising 1. what _Euclid_ hath said of _Lines_, Streight, Intersecting one another, and Parallel. 2. What he hath demonstrated of a _Single Triangle_, and of _Triangles Compared_ one with another. 3. What of the _Circle_, and its Properties. 4. What of _Proportions_ in Triangles and other Figures. 5. What of _Quadrats_ and _Rectangles_, made of Lines diversly {262} cut. 6. What of _Plane Superficies_'s. 7. What of _Solids_. After which follow the _Problems_. The _Definitions_ are put to each _Chapter_ as need requireth. The _Axioms_, because they are few, and almost every where necessary, are not thus distributed in _Chapters_. The _Postulata_, are not subjoyn'd to the _Axioms_, but reserv'd for the _Problems_, the Author esteeming, that they being _practical_ Principles, had only place in _Problems_. This for the _Order:_ As to the _Manner_ of Demonstrating, One and the same is observ'd in most Propositions; all with much brevity; to the end, that what is not of it self difficult, may not be made so, by multitude of Words and Letters.