VOL. VI.] PHILOSOPHICAL THANSACTIONS. 667 



direct, and that which is made by rays refracted. — Discoursing of refraction, he 

 declares, that the refraction of a visual ray in glass, to 30 degrees of inclination, 

 is proportional to the inclination of the ray, as far as sense is able to judge of it. 

 And that the inclination not exceeding 30 degrees, the angle of the refraction 

 of the ray which enters into glass, is about a third part of the angle of the in- 

 clination of the ray passing into the air : But that, the same inclination not ex- 

 ceeding 30 degrees, the angle of the refraction of the ray issuing out of the 

 glass into the air, is about the half of the angle of its inclination in the glass. 



The second part deliv ers the theory of the telescope in all its kinds : which is 

 ushered in by a history of the invention and antiquity of telescopes ; and by a 

 discourse concerning the difference of the ancient glasses from the modern.^ 

 This done, he explains the matter of this second part in 1 1 sections. 



The third part of this volume is subdivided into two, which the author calls 

 the positive, and mechanical. The positive teaches the actual construction of 

 telescopes, and their uses, and that in 12 sections. In these, among other 

 things, he treats of the use of telescopes in the observations of celestial objects: 

 Where the author enumerates the many excellent discoveries that by their 

 means have been made by modern astronomers : — Such as are, 1 . The con- 

 junction of Mercury with the sun. — 2. Venus having her phases like the moon. 

 —3. The body of the moon appearing like another earth, full of mountains and 

 valleys, seas, rocks, islands, lakes, forests and vast plains ; as also the libration 

 of the moon. — 4. Spots in the sun. — 5. The four satellites of Jupiter. — 6. A 

 satellite of Saturn, and rings about the same. — 7. Several belts about Jupiter, 

 and divers spots in Mars, Venus, &c. — 8. The milky way nothing but an innu- 

 merable company of small stars, near to one another. — g. The finding an 

 eclipse to begin and end sooner when observed with the naked eye, than when 

 seen with a telescope ; as also, that it appears always less by a digit, being ob- 

 served by the bare eye, than in reality. — 10. Pleiades consisting of many more 

 stars than seven. — 11. Orion having 80 other stars besides those three in his 

 belt, and the six in his sword: And the same having in his head 21, instead of 

 the one called the Nebuloso. — 12. The observ^ation of many new stars, as in 

 Cassiopaea, in Cete, in Cygno, Andromeda, &c. 



The other head is the mechanical, showing the several ways of forming and 

 polishing all sorts of glasses, that serve for telescopes ; which is done in six 

 sections. 



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