123 



edge of a piece of parallel aiul pellucid glass, it cannot escape 

 through its faces, because it is incident on tliem at an incidence 

 greater than that of total reflection. Looking through the 

 faces, therefore, the field of view is absolutely black, unless 

 there be bubbles or stride in the glass; but if a scale of any 

 kind be engraved on either of them with a diamond, the light 

 escapes through the cuts, and they appear luminous. The 

 division are 6", and the eye-piece has, of course, a position 

 circle. 



Dr. Robinson regrets that he had very few opportunities, 

 while at Parsonstown, of using the telescope, in consequence 

 of the unfavourable weather, and of the circumstances which 

 have been stated. Most of them, too, occurred while the spe- 

 culum was imperfect ; yet some facts which he observed may 

 be worth the notice of the Academy. 



In the moon may be mentioned that the wide surface at 

 the bottom of the Crater Albategnius is all strewed with mi- 

 nute blocks, not visible in the three feet with 500. The ex- 

 terior of the mountain Aristillus is all hatched as it were with 

 deep gullies radiating towards its centre ; and he was able to 

 confirm his former observations, that the bright streaks which 

 radiate from some craters (Kepler in this case) are not raised 

 above the surface. 



Jupiter was several times seen. The dark brown belts 

 presented, on February 20, a remarkable appearance ; they 

 were full of faint striae running nearly parallel to them, and 

 seemingly belonging to the brighter zones <5n each side. The 

 colour of the belts is deepest at the centre, and gradually dies 

 away towards the edge. This he regards as evidence that 

 they are seen through an atmosphere of considerable depth 

 and imperfect transparency. From this too, and from the fact 

 that the polar regions present a similar though less intense 

 shade, it is evident that the darker parts are the body of the 

 planet, and the brighter its clouds. 



Several nebulae, in addition to those which were men- 



