But it was felt that the strongest part of Herschel's case lay in his reference to the great nebula of Orion. He pointed out that amongst all the nebulae which might be reasonably assumed to be star-systems, a certain proportionality had always been found to exist between the telescope which first detected a nebula and that which effected its resolution into stars. And this was what might be expected to happen with star-systems lying beyond our galactic system. But how different is this from what was seen in the case of the Orion nebula. Here is an object so brilliant as to be visible to the naked eye, and which is found on examination to cover a large region of the heavens. And yet the most powerful telescopes had failed to show the slightest symptom of resolution. Were we to believe that we saw here a system of suns so far off that no telescope could exhibit the separate existence of the component luminaries, and therefore (considering merely the observed extent of the nebula, which is undoubtedly but a faint indication of its real dimensions) so inconceivably enormous in extent that the star-system of which our sun is a member shrinks into nothingness in comparison? Surely it seemed far more reasonable to recognise in the Orion nebula but a portion of our galaxy,-a portion very vast in extent, but far inferior to that 'limitless ocean of universes' presented to us by the other view.

And when Sir W. Herschel was able, as he thought, to point to changes taking place within the Orion nebula, it seemed yet more improbable that the object was a star-system.

But now telescopes more powerful than those with which the elder Herschel had scanned the great nebula were directed to its examination. Sir John Herschel, following in his father's footsteps, applied himself to the diligent survey of the marvellous nebula with a reflecting telescope eighteen inches in aperture. He presented the nebula to us as an object of which ' the revelation of the ten-feet telescope was but the mere rudiment.' Strange outlying wisps and streamers of light were seen, extending far out into space. Yet more strange seemed the internal constitution of the object. So strange, indeed, did the nebula appear, 'so unlike what had hitherto been known of collections of stars,' that Sir John Herschel considered the evidence afforded by its appearance as sufficient to warrant the conclusion of a non-stellar substance.

But this eminent astronomer obtained a yet better view of the great nebula when he transported to the Cape of Good Hope an instrument equal in power to that which he had applied to the northern heavens. In the clear skies of the southern hemisphere the nebula shines with a splendour far surpassing that which it has in northern climes. It is also seen far higher above the horizon. Thus the drawing which Sir J. Herschel was able to execute during his three years' residence at the Cape is among the best views of the great nebula that have ever been taken. But even under these favourable circumstances, Sir John records 'that the nebula, through his great reflector, showed not a symptom of resolution.'

Then Lassell turned his powerful mirror, two feet in diameter, upon the unintelligible nebula. But though he was able to execute a remarkable drawing of the object, he could discern no trace of stellar constitution.

In 1845 Lord Rosse interrogated the great nebula with his three-feet mirror. Marvellous was the complexity and splendour of the object revealed to him, but not the trace of a star could be seen.

The end was not yet, however. Encouraged by the success of the three-feet telescope, Lord Rosse commenced the construction of one four times as powerful. After long and persistent labours, and at a cost, it is said, of thirty thousand pounds, the great Parsonstown reflector, with its wonderful six-feet speculum, was directed to the survey of the heavens. At Christmas, 1845, while the instrument was yet incomplete, and in unfavourable weather, the giant tube was turned towards the Orion nebula. Professor Nichol was the first who saw the mysterious object as pictured by the great mirror. Although the observation was not successful so far as the resolution of the nebula was concerned, yet Nichol's graphic account of the telescope's performance is well worth reading:

'Strongly attracted in youth by the lofty conceptions of Herschel [he writes], I may be apt to surround the incident I have to narrate with feelings in so far of a personal origin and interest: but, unless I greatly deceive myself, there are few who would view it otherwise than I. With an anxiety natural and profound, the scientific world watched the examination of Orion by the six-feet mirror; for the result had either to confirm Herschel's hypothesis, in so far as human insight ever could confirm it; or unfold among the stellar groups a variety of constitution not indicated by those in the neighbourhood of our galaxy. Although Lord Rosse warned me that the circumstances of the moment would not permit me to regard the decision then given as absolutely final, I went in breathless interest to the inspection. Not yet the veriest trace of a star ! Unintelligible as ever, there the nebula lay; but how gorgeous its brighter parts! How countless those streamers branching from it on every side ! How strange, especially that large horn on the north, rising in relief from the black skies like a vast cumulous cloud! It was thus still possible that the nebula was irresolvable by human art; and so doubt remained. Why the concurrence of every favourable condition is requisite for success in such inquiries may be readily comprehended. The object in view is to discern, singly, sparkling points, small as the point of a needle, and close as the particles of a handful of sand; so that it needs but the smallest unsteadiness in the air, or imperfection in the shape of the reflecting surface, to scatter the light of each point, to merge them into each other, and present them as one mass.'