The text of this book has been preserved in its original form apart from correction of two typographic errors: embarrasment → embarrassment, Cassegranian → Cassegrainian. Inconsistent hyphenation has not been altered. A lengthy preliminary section concerning the Smithsonian Institution precedes the actual subject matter. A black dotted underline indicates a hyperlink to a page, illustration or footnote (hyperlinks are also highlighted when the mouse pointer hovers over them). Page numbers are shown in the right margin and footnotes are located at the end. Footnotes are located at the end.
The original blank cover has been modified by adding a title and is placed in the public domain.