Page:Popular Science Monthly Volume 5.djvu/280

266 of the nebula and its contained stars. There was a large number of errors in this catalogue, and Boud's work was sharply criticised by O. Struve, whose "Memoir on the Nebula of Orion" appeared in 1862. Struve's work, which was a revision and an extension of the work of Liapanoff (done at Kazan with a 9-inch retractor), was executed very carefully with the 15-inch telescope of Pulkova; and some of his strictures on the elder Bond's work were so severe as to induce G. P. Bond, his son, then Director of Harvard College Observatory, to take up his father's work, to complete and amend it. This he has done in a most admirable monograph, which is a model of its kind. We have already spoken of his engraving of the nebula, and its excellence is only commensurate with the completeness of the whole of the memoir.

Fig. 7 represents the small stars in the now familiar ground near the trapezium.



It will be seen how much fuller this map is than Lassell's, which contains more small stars probably than any of the preceding ones.

Lord Rosse's great reflecting telescope of 6-feet aperture was employed at various times, between 1848 and 1867, in making drawings of the Orion nebula; and we have, as the results of the work, two great engravings, upon which much care has been spent.

These certainly differ in many important points from the preceding drawings which were made by reflectors (and experience will show us that it is not easy, critically, to compare drawings made by reflectors and by refractors); but this is simply a proof that the drawings of