146 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1912. 



To sum up, the great nebula of Orion is a very complicated object, 

 very rebellious against graphical representation by which means we 

 had hoped to show by a comparison of drawings what changes may 

 have taken place during the course of a century. The early drawings 

 have in this respect very little value and the elaborate discussion 

 which Holden based upon the sketches of Bond has not in general 

 been found convincing. 



This nebula departs too far from a globular form or rather from a 

 figure of rotation to be taken as giving support to the Laplacian 

 hypothesis. No one could trace in it a prelude to the formation of a 

 narroAv and regular ring surrounding a larger central body. Several 

 annular nebulae were noted by W. Herschel, but among them not one 

 had a nucleus of any importance. 



If we must find in the sidereal universe a picture of what took place 

 in our system, then we would have greater hope of finding it among 

 the planetary nebulse. In the smaller telescopes they appear as 

 small round, somewhat brilliant, diffused spots, but in stronger 

 instruments like bright stars embedded in dense atmospheres. But 

 such systems were too small and too distant to tell us much of 

 the details of their structure before spectroscopic methods were 

 developed. 



Such was the condition of affairs when Lord Rosse, in 1850, showed 

 the existence of a distinct series of nebulae, having besides the cen- 

 tral nucleus several successive envelopes. But these envelopes, 

 instead of being separate and concentric, as the advocates of Laplace's 

 hypothesis would have expected, were spiral in form. They showed 

 streamers, growing progressively larger, at first in the direction of 

 the radius, then curved around all in the same sense. No theory 

 had predicted such an appearance. 



The instrument used by Lord Rosse and made under his direction 

 was a gigantic telescope, 6 feet in aperture, a size not since surpassed 

 despite many courageous attempts. Judging from drawings, it could 

 have been used only near the meridian. Nor was sufficient protec- 

 tion provided against the weather, either for the observer or the 

 mirror. The necessary access to the upper part of the tube was 

 possible only by the nse of heavy and complicated machinery. 

 Such a piece of apparatus required the assiduous and careful maneu- 

 vering of several assistants. Official astronomers, with strict limita- 

 tions and limited means, could obtain such cooperation only with 

 great trouble and for very little time. Is it necessary to seek further 

 for the reason why the great instruments of Lord Rosse and the 

 Herschels, despite their great services, had such a short career and 

 were used only by their makers? 



