11, What is the _Sphere of Activity_ of Cold, or the Space, to whose extremities every way the Action of a cold Body is able to reach: where the difficulty of determining these limits, together with the causes thereof, being with much circumspection mentioned, it is observed, that the _Sphere of Activity_ of Cold is exceeding narrow, not only in comparison of that of Heat in Fire, but in comparison of, as it were, the _Atmosphere_ of many odorous Bodies; and even in comparison of the _Sphere of Activity_ of the more vigorous Loadstones, insomuch, that the Author hath doubted, whether the Sense could discern a Cold Body, otherwise then by immediate Contract. Where several Experiments are delivered for the examining of this matter, together with a curious relation of the way used in _Persia_, though a very hot Climate, to furnish their _Conservatories_ with solid pieces of Ice of a considerable thickness: To which is added an Observation, how far in Earth and Water the Frost will pierce downwards, and upon what accounts the deepness of the Frost may vary. After which, the care is inculcated, that must be had, in examining, whether Cold may be diffused through all _Mediums_ indefinitely, not to make the Trials with _Mediums_ of two great thickness: where it is made to appear, that Cold is able to operate through Metalline Vessels, which is confirmed by a very pretty Experiment of making _Icy Cups_ to drink in, whereof the way is accurately set down. Then are related the Trials, whether, or how, Cold will be diffused through a _Medium_, that _some_ would think a _Vacuum_, and which to _others_ would seem much less disposed to assist the diffusion of Cold, than Common Air it self. After which follows a curious Experiment, shewing whether a Cold Body can operate through {51} a _Medium_ actually hot, and having its heat continually renewed by a fountain of heat. 12, How to estimate the solidity of the Body of Ice, or how strong is the mutual adhesion of its parts? and whether differing Degrees of Cold may not vary the Degree of the compactness of Ice. And our Author having proceeded as far as he was able towards the bringing the strength of Ice to some Estimate by several experiments, he communicateth the information, he could get about this matter among the Descriptions that are given us of cold Regions: and then he relateth out of Sea-mens _Journals_, their Observations touching the insipidness of resolved Ice made of Sea-water; and the prodigious bigness of it, extending even to the height of two hundred and forty Foot above water, and the length of above eight Leagues. To which he adds some promiscuous, but very notable Observations concerning Ice, not so readily reducible to the foregoing Heads: _videlicet_, Of the blew colour of Rocky pieces of Ice; and the horrid noise made by the breaking of Ice, like that of Thunder and Earthquakes, together with a Consideration of the cause, whence those loud Ruptures may proceed.