68 
LOED OXMANTOWN ON THE GEEAT NEBULA IN OEION. 
In connexion with this subject it may not be uninteresting to compare the observations 
of former observers with each other and with our own. 
Sir J. Herschel in his paper of 1825 discusses the differences between his own 
drawings and those of Huygens, Picard, Messier, and Le Gentil, and thinks that the 
first three, when compared with his own, tend to show a gradual diminution or conden- 
sation of the nebulosity ; but Le Gentil’s, which was older than Messier’s, represents 
it just as he himself saw it. 
We next come to Sir J. Hersciiel’s paper of 1837, in which he says that although to 
any one who has not viewed this object through powerful telescopes the differences 
between the various drawings, including his own of 1824 and 1837, may seem great, and 
tend to convey a strong impression of great and rapid changes undergone by the nebula 
itself, yet, after carefully comparing his own two drawings, he comes to the conclusion 
that the differences are not greater than he is disposed to attribute to his own inexpe- 
rience in such delineations in 1824, to the greater care bestowed on the later drawing, 
and especially to the advantage of better local situation and superior defining power, &c. 
of the telescope at the latter date (Cape Observations, page 31). There are three points, 
however, to which he directs attention, but in the case of two only of them is he inclined 
to conclude that there is any evidence of change ; these points are — 
1. The form and position of the nebula oblongata between 127 x and 129J. 
2. The position of the nebulous spur between 111 and 122. 
3. The form of the nebula round 108. 
In 1 824 Sir J. Herschel saw the nebula oblongata as a “ tolerably regular oval,” 
nearly in a line between the stars 120 and 136, whereas in his drawing of 1837 it is 
irregular in outline, and decidedly above the line through 120 and 136. 
With respect to the form of the nebula oblongata, the brighter part forms a “ tolerably 
regular oval,” but when the fainter parts are included it seems to be more of the form 
given in Herschel’s drawing of 1837. It is therefore quite possible, even probable, 
that Herschel would have seen it oval in 1825, but long and slightly curved upwards 
with the superior means at his disposal in 1837, without any change of form having 
taken place in the interval ; but as regards its position it appears to be now entirely 
above the line 120-136. 
With regard to the nebulous spur between 111 and 122, diagrams which he made in 
1832 and 1834 represent it as “ running directly from 135 to 111 and forming a com- 
plete hook no way disjoined from the proboscis.” In 1837 he saw it “neither 
joined to the proboscis nor directed towards 135, but rather towards a point one-third 
the distance from 135 to 126 ” near the position of 131. Herschel’s second drawing 
appears to agree very fairly with the accompanying one in this respect ; perhaps the 
superior definition of Herschel’s instrument in 1837, a better atmosphere, and the 
greater * meridian altitude of the object enabled Herschel to perceive the interval 
between this spur and the proboscis which had escaped his notice in 1832 and 1834. 
* This last applies to the diagram of 1832 only. 
