But, _saith he_, let us consider, only a Glass of 300 foot, to see, what is to be hoped of that, and to know at least the difficulty, to be met with in making a Glass only of that Length. A Glass then of 300 foot, according to his Table, must have more than 8 inches _Aperture_, which maketh but 16 minuts of its _Circle_, and it should have more than 11 inches, if it be an excellent one. If Mr. _Hook_ (adds he) did use but his _Ring_ of 6 inches, which he would use from twelve to an hundred foot Glass, the _Inclination_, which the _Axis_, or _Mandril_, that bears his Glass, should have, should be but 16 minuts, and the _Curvity_ of the Glass would be less than the eighth part of a Line, and if he should use a bigger, the _Inclination_ would be proportionable. Whence it may be judged (continues he) that we are yet very far from seeing _Animals &c._ in the _Moon_, as Monsieur _Des Cartes_ gave hope, and Mr. _Hook_ despairs not of. For, he believes by what he knows of _Telescopes_, that we are not to look for any above 300 or 400 foot at most; and he fears, that neither _Matter_ nor _Art_ will go even so far. When therefore (_saith he_) a Glass of 300 foot should bear an Eye-glass of 6 inches (which would appear wonderful) it would magnifie but 600. times in _Diameter_, that is, 360000 times in _Surface_: but suppose, that such could be made, as would magnifie a 1000 times in _Diameter_, and 1000000. of times in _Surface_, admitting there were but 60000 leagues from the _Earth_ to the _Moon_, and that the smalness of the _Aperture_ of the Glasses (which yet would diminish the Light more than 36 times) and the obstacle of the Air were not considered, we should not {61} see the _Moon_, but as if we were a 100, or at least, 60. leagues distant from her without a Glass. He here wishes, that those, that promise to make us see _Animals_ and _Plants_ in the Moon, had thought on what our naked Eyes can make us discern of such Objects, only at 10 or 12 leagues distance. But this he would not have understood as a discouragement from searching with all care and earnestness after the means of making long _Telescopes_, or of facilitating the working thereof; but only as an Advertisement to those, who light upon the _Theory_ of any _Engine_, not to expose it presently as possible and useful, before they have tried it, or if it have succeeded in small, not to endeavour to persuade, that it will also succeed in great.