POPULAR SCIENCE MONTHLY.
American books on surveying have heretofore been prepared primarily as texts for class use, rather than for the use of the field engineer. This point of view is reversed in the volume of 900 pages, by Herbert M. Wilson, entitled 'Topographic Surveying, including Geographic, Exploratory and Military Mapping,' recently issued by John Wiley & Sons. It sets forth, in the main, the practise of the U. S. Geological Survey, and many of the illustrations have been derived from the publications of that bureau, the colored ones being printed from copper plates owned by the Government. Field work, with the plane table, the transit and stadia, the level and office methods of mapping occupy nearly one-half of the volume; about 300 pages are devoted to geology and astronomy, and the remainder to photography, camping, and the subsistence and health of field parties. In no book heretofore issued are the practical details of topographic work discussed with such fulness as here, and the numerous tables will be found of great assistance in facilitating computations. Indeed, a special effort seems to have been made in the direction of tables, some of which might well have been omitted; for instance, the space devoted to the table of Peirce's criterion for the rejection of observations would have been better filled by elementary matter on the method of least squares, and the table for the values of 0.046d, when d=10, 20, 30, etc., seems a reflection on the mathematical knowledge of the reader. The book is in general clearly written, although the frequent use of italics seems to indicate that the author was often apprehensive that he might be misunderstood. It is a valuable supplement to the text-books of the engineering colleges.
'Road Making and Maintenance,' by Thomas Aitken (London, Griffin & Co.), deals largely with European practise in street construction. The country roads of England are as a rule better than those of the United States, having been earlier built and more systematically repaired, while great attention is paid to securing uniformity of surface. An instrument called the viagraph is described by the author, which takes an automatic record of the inequalities of the street surface and gives the sum of all the vertical depressions found in paving over a mile. A road having 15 feet of such depressions per mile is called excellent, while a fair road has 40 or 50 feet per mile, and a passable one 60 or 80 feet per mile. The cost of this viagraph is moderate, and it is only necessary to drag it along the street in order to obtain the authentic record. It is surprising to learn that wooden pavements still continue to be laid in English towns, while brick pavements are practically untried. On questions of city streets American practise seems fully abreast of that of England now that the necessity of good foundations of concrete is fully recognized. *Street Pavements and Paving Materials,' by George W. Tillson (New York, Wiley & Sons), sets forth modern American practise in an exhaustive manner, giving specifications in use in different cities for different kinds of pavements. The first asphalt pavement laid in the United States was in 1870; great difficulties were met in adapting asphalt to climate and traffic, but these have