in this Passage of the same _Paragraph_, of which sort are also those difficulties he raises about _Long Glasses_, which are commonly known to such, as are conversant in making them _It would be convenient also_ (these are my words) _and not very chargeable, to have four or five several Tools: One,_ &c. _And, if curiosity shall ever proceed so farr, one for all lengths, between 1000. and 10000. foot long; for indeed, the _Principle_ is such, that supposing _the Mandrils well_ made, and of a good length, and supposing _great care_ be used in working and polishing them, I see no reason, but that a Glass of 1000. nay, 10000. foot long may be made, as well as one of 10. For, the reason is the same, supposing the _Mandrils_ and _Tools_ be made sufficiently strong, so that they cannot bend; and supposing also that the Glass out of which they are wrought, be capable of so great a regularity in its parts, as to its Refraction._ But next, I must say that his _Objections_ to me, seem not so considerable, as perhaps he imagines them. For, as to the possibility of getting Plates of Glass thick and broad enough without veins, I think _that_ not now so difficult here in _England_, where I believe is made as good, if not much better Glass for _Optical Experiments_, than ever I saw come from _Venice_. Next, though it were better, that the thickest part of a long _Object-Glass_ were exactly in the middle, yet I can assure Monsieur _Auzout_, that it may be a very {66} good one, when it is an Inch or two out of it. And I have a good one by me at present, of 36. foot, that will bare an _Aperture_, if _Saturn_ or the _Moon_ in the _twilight_, be look'd on with it, of 31/2 Inches over, and yet the thickest part of the Glass is a great way out of the middle. And I must take the liberty to doubt, whether ever my _Animadversor_ saw a long Glass, that was otherwise; as he might presently satisfie himself by a way I could shew him (if he did not know it) whereby the difference of the thickness of the sides might be found to the hundreth part of a Line.