588 Royal Irish Academy. 



The solid speculum showed a Lyrre round and well denned, with 

 powers up to 1000 inclusive, and at moments even with 1600 ; but 

 the air was not fit for so high a power on any telescope. Rigel, two 

 hours from the meridian, with 600, was round, the field quite dark, 

 the companion separated by more than a diameter of the star from its 

 light, and so brilliant that it would certainly be visible long before 

 sunset. £ Orionis, well defined, with all the powers from 200 to 

 1000, with the latter a wide black separation between the stars ; 32 

 Orionis and 31 Canis minoris were also well separated. 



It is scarcely possible to preserve the necessary sobriety of lan- 

 guage, in speaking of the moon's appearance with this instrument, 

 which discovers a multitude of new objects at every point of its sur- 

 face. Among these may be named a mountainous tract near Ptolemy, 

 every ridge of which is dotted with extremely minute craters, and two 

 black parallel stripes in the bottom of Aristarchus. 



The Georgian was the only planet visible ; its disc did not show 

 any trace of a ring. As to its satellites, it is difficult to pronounce 

 whether the luminous points seen near it are satellites or stars with- 

 out micrometer measures. On October 29th, three such points were 

 seen within a few seconds of the planet, which were not visible on 

 November 5 th ; but then two others were to be traced, one of which 

 could not have been overlooked in the first instance, had it been in 

 the same position. If these were satellites, as is not improbable, there 

 would be no great difficulty in taking good measurement both of 

 their distance and position. 



There could be little doubt of the high illuminating power of such 

 a telescope, yet an example or two may be desirable. Between e l 

 and e 2 Lyrae, there are two faint stars, which Sir J. Herschel (Phil. 

 Trans. 1824) calls " debilissima," and which seem to have been, at 

 that time, the only set visible in the twenty-foot reflector. These, at 

 the altitude of 18°, were visible without an eye-glass, and also when 

 the aperture was contracted to twelve inches. With an aperture of 

 eighteen inches, power 600, they and two other stars (seen in Mr. 

 Cooper's achromatic of 13*2 aperture, and the Armagh reflector of 15) 

 are easily seen. With the whole aperture, a fifth is visible, which 

 Dr. Robinson had not before noticed. Nov. 5th, strong moon- 

 light. 



In the nebula of Orion, the fifth star of the trapezium is easily 

 seen with either speculum, even when the aperture is contracted to 

 eighteen inches. The divided speculum will not show the sixth with 

 the whole aperture, on account of that sort of disintegration of large 

 stars already noticed, but does, in favourable moments, when con- 

 tracted to eighteen inches. With the solid mirror and whole aper- 

 ture, it stands out conspicuously under all the powers up to 1000, 

 and even with eighteen inches is not likely to be overlooked. 



Comparatively little attention was paid to nebulae and clusters, 

 from the moonlight, and the superior importance of ascertaining the 

 telescope's defining power. Of the few examined were 1 3 Messier, 

 in which the central mass of stars was more distinctly separated, and 

 the stars themselves larger than had been anticipated; the great 



