Royal Astronomical Society. 231 



300 years. As the angle of position has only altered 24° in 63 years, 

 the result is rather uncertain. 



Mr. Hind points out several double stars which are promising 

 subjects for investigation; £Scorpii, 12Lyncis, £ Aquarii, 36 An- 

 dromeda?, 85 Persei, ij Tauri, w 1 Cancri, <r 2 Ursse Majoris, 157 Lyncis, 

 49 Serpentis, oDraconis, and 2 460, 520, 1126, 1457, 1757, 1819, 

 2107, 2120, 2438. He conceives that £ Scorpii probably revolves in 

 a very elongated ellipse. 



Suggestions for Improving the Manufacture of Optical Glass. By 

 James Nasmyth, Esq. 



Mr. Nasmyth, after remarking, for our encouragement, that the 

 problem is possible, since large discs of homogeneous glass are made 

 elsewhere, expresses his conviction that the proper materials in suf- 

 ficient purity are at our command, and that the difficulty is in the 

 mode of effecting perfect combination and vitrification. 



He proposes to carry the heat of the furnace to the highest prac- 

 ticable degree, thus ensuring perfect fusion and fluidity, and then, by 

 maintaining the heat for a considerable time, to give the particles 

 time to arrange themselves in their order of density. He would then 

 lower the heat so gradually as to avoid disturbing their arrangement, 

 but not so slowly as to endanger its vitreous quality. The melting- 

 pots should be cylindrical in form, and as deep as prudence will 

 permit. The mass, when cool, is to be sawn across in parallel slices. 

 In this way Mr. Nasmyth conceives that discs nearly homogeneous 

 would be procured, and at any rate that the density would be uniform 

 through each horizontal section, which perhaps would be sufficient 

 for optical purposes. If there be any tendency to unite in definite 

 proportions, it is clear that the circumstances described would fa- 

 vour the combination. 



Without venturing to give a positive opinion on such a subject, 

 the method seems founded on rational principles. It is high time 

 some vigorous attempt should be made to manufacture optical glass 

 in this country. The foreign supply is scanty, and often of indiffer- 

 ent quality. At Munich, finished object-glasses, only, are furnished ; 

 the price is high, and the telescopes not always of corresponding 

 quality. It is nearly a century since Dollond discovered the prin- 

 ciple of achromatism, and constructed his admirable telescopes ; and 

 it may be doubted whether the manufacture of optical glass has since 

 advanced one step in this country. The great bar to improvement, 

 the vexatious excise laws, is removed ; and the first person who can 

 restore this country to her original pre-eminence in optical glass- 

 making, will not merely derive a large pecuniary recompense, but be 

 entitled to the gratitude of every lover of astronomical science. 



At the close of the meeting Mr. Sheepshanks gave a short account 

 of the origin and construction of instruments on the repeating prin- 

 ciple, expressing an opinion that, though the improved construction 

 and division of astronomical and geodesical instruments had in later 

 years taken away much of the original value of this invention, yet 

 that, under some circumstances, a repeating stand for a theodolite 

 or an astronomical circle repeating in altitude might be useful. 



