# A Description of Dr. Christopher Wren's Engin, Designed for Grinding Hyperbolical Glasses; As It Was in a Manner Promised Numb. 48. p. 962 **Author(s):** Christopher Wren **Year:** 1669 **Journal:** Philosophical Transactions (1665-1678) **Volume:** 4 **Pages:** 4 pages **Identifier:** jstor-101029 **JSTOR URL:** --- PHILOSOPHICAL TRANSACTIONS. November 15. 1669. The Contents. A Description of Dr. Christopher Wren's Engin, designed for Grinding Hyperbolical Glasses. Some Inquiries concerning the Salt-springs at Nantwich, answered. An Extract of a Letter, concerning the Death of the Bigg-breasted Woman, discoursed of in Numb. 52. An accompt of some Books: I. CERTAIN PHILOSOPHICAL ESSAYES, and other TRACTS by the Honorable ROBERT BOYLE: The Second edition, enlarged. London; printed for H. Herringman in the New-Exchange; A. 1669. II. DEL MOVIMENTO DELLA COMETA, apparsa A. 1664: Da PIETRO MARIA MUTOLI, in Pisa, in 4°. III. ERASMI BARTHOLINI de COMETIS A. 1664. & A. 1665. Opusculum. Hafniæ in 4°. IV. SYLVA & POMONA, reprinted with Enlargements, by I. EU ELYN. Esquire &c. A Description Of Dr. Christopher Wren's Engin, designed for grinding Hyperbolical Glasses; as it was in a manner promised Numb. 48. p. 962. We shall give it in the Author's owne words, as followeth. Sint tria Corpora terendo idonea, P. Q. R; quorum P. & Q. sint aqualia & Columnari forma, R vero Corpus Lenti-forme. P. rotetur circa axin A B; Q., circa C D; & R, circa E G. Sint autem A'B & C D in diversis Planis, ita tamen ut EG prolnsta, sit ad rectos angulos utrique A B & C D: accedant de- nique ad se invicem Corpora, prout opus fuerit, servata tamen ea- dem inclinatione & siti Axium. Dico, ex revolutione & mutua attritione Corporum prius positio- rum exurgere nova corpora Geometrica, quorum P & Q erunt Cylindroidea Hyperbolica aqualia, R vero Conoides Hyperbo- licum, specie & magnitudine datum. Demonstrationem in promptu habemus, nec non Modulum ipsius Machina, terendis Lentibus Hyperbolici destinatis; quam opcro- sa pictura & prolixa explicatione describere, mihi & artifici ma- gis fuerit molestum, quam Daedalo cuivis sagaci similim ad-inve- nire. Postquam enim exposita jam sunt principia Geometrica, faci- le crit conjicere, quale sit Instrumentum; nempe, tres sunt Ta- bulae oblongae, plane, vulvae, labiles, & sibi invicem impositae: Insima & Media sustinent inaequalia Capitula (sive Ansa mam- phur sustinentes) alternativae posita; id postulat utrinque mamphu- ris obliquitas & quasi decussatio: Summa Tabulae aequalia sunt Ca- pitula in longum Tabulae disposita; & perforato citimo Capitulo mamphur transmittitur. Omitto rotas, rotulas, lora, pondera, cochle- as, & reliqua admodum expeditum & Machina firmiter linem ne- cessaria. P pertinet ad insimam Tabulam; Q ad mediam; R, ad summam. R, Lens est vitrea: Q, Modulus Lentem tenens; P, Formula Modulum corrigens; que, dum motu obliquo, & diver- so a motu tam Lentis quam Moduli, fertur, delet continuo & dete- rit, quicquid viti imperimitur in Modulum ex Lentis & Mate- ria attritione. Quare, cum ad o simplex & spontanea sit ista Hyperbolici Co- noidis genitura, ex solis nempe motibus Circularibus; cumque motus sit duplex & varius, credibile est, Lentes Hyperbolicas ex hifice Principiis vel nullis fore explicandas. Some Inquiries Concerning the Salt-Springs and the Way of Salt- making at Nantwich in Cheshire; Answer'd by the Learned and Observing William Jackson Dr. of Physick. 1. What is the depth of the Salt-springs? The depths are various, in some places not above 3. or 4. yards. In our Town of Nantwich, the Pit is full 7. yards from the