¶ On our shelves is the most complete stock of engineering, scientific, technical and industrial books in the United States. A large number of these we publish and for an ever increasing number we are the sole agents. ¶ _All inquiries are cheerfully and carefully answered and complete catalogs as well as special lists are sent free on request._ D. Van Nostrand Company _PUBLISHERS AND BOOKSELLERS_ 8 WARREN STREET NEW YORK Transcriber's Notes: Passages in italics are indicated by _italics_. Subscripted characters are indicated by {subscript}. The following misprints have been corrected: "imgaes" corrected to "images" (page 128) "bove" corrected to "above" (page 177) "verticle" corrected to "vertical" (page 239) "colo" corrected to "color" (Index) Other than the corrections listed above, inconsistencies in spelling and hyphenation have been retained from the original. The inverted "8" and "S" characters at the top of page 45 cannot be properly represented in this text version.