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British Association for the Advancement of Setence. 285 
or 4” in diameter. Many of them occur in crowded parts of the 
milky way, with not fewer than 80 or 100 stars in the field of 
view at once. 'The drawings are copies of much more elaborate 
originals, and merely selected from a greater collection, illustra- 
ting three of the most singularly constituted nebule in the S. 
Hemisphere, viz. 9 Orionis, 4 Argis and 30 Doradis. Sir J. ex- 
plained. how, by means of a small achromatic collimator placed 
inside his great sweeping telescope, he was able to obtain nearly 
the same precision ‘as was to be had in fixed observations; al- 
though from the ropes and wooden frame with which ics was 
mounted, it was ‘subjected to great hygrometric and pyrometric 
changes of form and position. These changes, by affecting alike 
the cross of the collimator, and the object, were readily detected 
and corrected.—Dr. Robinson, spoke in praise of the accuracy of 
the positions given in ‘Sir J. Herschel’s catalogues; and in favor 
of the application of reflecting telescopes to divided instruments. 
Notwithstanding the great increase in late years, of the size of 
achromatics, it seemed improbable that they would ever reach a 
magnitude which could not be easily overmatched by reflection. 
Something to this effect had been done in Ireland. In his. own 
observatory was a reflector of 15 inches aperture, applied to an 
equatorial of cast iron, which gave polar distances with a proba- 
ble error of about 6 seconds, and right. ascensions to the ultimate 
reading of the hour circle verniers. The artist who executed this, 
had since made a reflecting transit of six inches aperture, which 
_ performed well, and its collimator was not affected by reversion. 
Sir J. Herschel remarked that :the only change in a nebula, 
which he had-yet noticed, was in that of Orion. A small trans- 
verse strip, which, when he first figured. that nebula, was straight, 
had become parved, and showed a knotty” appearance, which cer- 
tainly it-did not possess before.” ~ 
Remarkable Phenomena if Halley s Comet.—Sir J. Herschel 
related the following. One of the most interesting series of ob- 
servations, I had to make at the Cape of Good Hope, was that of 
Halley’s Comet. This comet is the great glory of modern calcu- 
lation. ‘Fo see the predicted return of such a body now verified 
for the second time, true to a single day,—nay, to ‘a few hours— 
of his appointed time, after an absence of 75 or 76 years, during 
_ which it has been subjected to the unceasing perturbations of all 
the planets, and especially persecuted by Jupiter and Saturn, 
