But to remove all doubt, that this Inequality is caused by the Retardment of the Light, he demonstrates, that it cannot come from any Excentricity, or other Cause of those that are commonly alledged to explicate the Irregularities of the _Moon_, and the other Planets; though he be well aware, that the first _Satellit_ of _Jupiter_ was Excentrick; and that, besides his Revolutions were advanced or retarded, according as _Jupiter_ did approach to or recede from the Sun; as also, that the Revolutions of the _Primum Mobile_ were unequal: Yet, saith he, these three last Causes of Inequality do not hinder the first from being manifest. _An introductory _Essay_ to the Doctrine of _Sounds_, containing some Proposals for the improvement of _Acousticks_; As it was presented to the _Dublin Society_, Nov. 12. 1683, by the Right Reverend Father in God _Narcissus_ Lord Bishop of _Ferns_ and _Leighlin_._ Being to treat of the Doctrine of _Sounds_, I hold it convenient to premise something in the general, concerning this Theory; which may serve at once to ingage your Attention, and excuse my Pains, when I shall have recommended them, as bestow'd on a Subject not altogether useless and unfruitful. And for this purpose I shall omit to speak any thing of the _Excellency_ of the Matter in Hand; though it might be celebrated by Arguments drawn from several Topicks, and particularly from this, that new Discoveries and Improvements may be made, both as to the _Generation_, _Propagation_ and _Reception_ of Sounds into the Sense; which, in a peculiar manner agrees to this, above the Object of any other Sense whatsoever. I shall, I say, omit these things, and apply my self wholly to the _Usefulness_ of the Theory, that we are now falling upon, which I think cannot better be discovered, than by making a comparison 'twixt the Senses of _Seeing_ and _Hearing_, as to their Improvements. I mean, by shewing, that this latter of _Hearing_ is capable of all those improvements which the Sense of _Seeing_ has receiv'd from Art, besides many more advantages that the _Ear_ may enjoy, by the help of our Doctrine, above the _Eye_; all which moreover will be of as great benefit to Mankind, as any thing that _Opticks_ have yet discover'd, if not of greater; which, with some other pre-eminencies that it has upon another Score, will happily render _Acousticks_ the nobler Science of the two. In order to the making good what I but now premised of the Comparison of these two Faculties of _Seeing_ and _Hearing_, as to their Improvements, I observe; That _Vision_ is threefold, _Direct_, _Refracted_, and _Reflex'd_; answerable whereunto we have _Opticks_, _Dioptricks_, and _Catoptricks_.