A defence of the doctrine touching the spring and weight of the air propos'd by Mr. R. Boyle in his new physico-mechanical experiments, against the objections of Franciscus Linus ; wherewith the objector's funicular hypothesis is also examin'd, by the author of those experiments.

The 4. Experiment.

In the Fourth Experiment, touching the swelling of a Bladder upon the removal of the ambient Air; and proportiona∣bly to that removal our Author objects nothing against the Ex∣plication we give of it by the Spring of the Air included in the Bladder, and distending it according as the pressure of the ambi∣ent Air is weakned. But he endeavours also to explicate it his way, to which he sayes this circumstance does excellently agree, that upon the regress of the external Air into the Receiver, the tumid Bladder immediately shrinks, because (saith he) by such ingress of the external Air, the Air in the Receiver, which drew the sides of the Bladder outward from the middle of it, is re∣lax'd. Which Explication whether it be more natural then ours (that ascribes the shrinking of the Bladder to the pressure of the Air that is let into the Receiver) let the Reader judge, who has considered what we have formerly objected against the Exa∣miners Funiculus, and the Relaxation of it upon the admission of Air.

As for the reason likewise he adds, why a perforated Bladder does not also swell, namely, that by the hole, how little soever,

the included Air is suck'd out by the rarefi'd ambient, we leave it to the impartial Reader to consider whether is the more genu∣ine Explication, either ours (against which he has nothing to ob∣ject) or his, which to make clearly out he ought (according to what we formerly noted disputing against his Funiculus) to shew us what kind of strings they are; which though, according to him, strongly fastned to the inside of the Receiver and the superfi∣cies of the Bladder, must draw just as forcibly one as another, how long soever they be without the Bladder in comparison of those that within the Bladder draw so as to hinder the diduction of its sides. For Experience shews, that in a perforated Bladder the wrinkles continue as if there were no drawing at all.

And though he could describe how such a string may be con∣text, yet our Explication will have this advantage in point of probability above his, That whereas he denies not that the Air has Spring and Weight, as we deny his Funiculus to have any other then an imaginary existence; and whereas he acknow∣ledges that by the Instrument the Air about the Bladder is ex∣hausted; to shew that there needs no more then that, and conse∣quently no Funiculus, to draw asunder the sides of the Bladder, we can confirm our Explication by the formerly mentioned Ex∣periment of the ingenious Paschall, who carrying a flaccid Foot-ball from the bottom to the top of a high Mountain, found it to swell proportionably as he ascended, and as the weight and pres∣sure of the ambient Air decreased, and likewise to shrink again as he descended. And yet in this case there is no recourse to be had to a Funiculus of violently-rarefi'd Air to draw asunder eve∣ry way the sides of the Foot-ball. But however the Examiner will be able to defend his Explication, it may suffice us that he has objected nothing against ours.