470 Book Notices. [J. F. I.,

they go. Under cer tain conditions, which are named in the letter~ the layer of dust reaches h igher and h igher every successive day. Dur ing long, dry summers in India it reaches to 7,000 feet wi th a well-defined upper surface t ha t is h igher in the day-t ime than at night- t ime. This is a general explana- t ion of dry haze weather and applies to Indian summer also. The reason why we have more of such weather in the au tumn is because there is then less horizontal wind and less r is ing air. W.

B O O K N O T I C E S .

,4merican S landard Specifications f o r S led . By Albert Ladd Colby, Mem- ber of Committee No. i, of the American Section of the In te rna t iona l Association for Test ing Materials. Second edition, t~aston, Pa.: The Chemical Publ i sh ing Co., 19o2. (Price, $I.IO.)

Mr. Colby gives a review of the work of Committee No. i of the American Section of the In te rna t iona l Association for Test ing ~¢laterials, showing how the i r proposed specifications were arrived at from the specifications in use. He refers to the general discussion, bo th at home and abroad, of these pro- posed specifications dur ing the past two years, and the i r final adoption by the American Section last summer.

A general review is then given of the requi rements of the specifications, wi th the reasons which governed the Commit tee in its decisions, and takes up each of the following headings :

(I) Process of Manufacture. (2) Chemical Properties. (3) Physical Properties. (4) Test Pieces and Methods of Test ing. (5) Finish and Variat ion in Weight. (6) Branding. (7) Inspect ion. After this there is a review of each of the nine specifications. These

reviews are excel lent and give a clear, concise s ta tement of the condit ions governing the work. The specifications are becoming the recognized stand- ards of this country; the Rail Specifications, with some modifications, hav ing recent ly been adopted by the American Railway Engineers and Main- tenance of Way Association as the i r standard.

The book is a good addit ion to our engineer ing l i terature on the subjects treated, and its price is only moderate. W . R . W .

A n n u a i m p o u r Pan 19o2 , publi~ par le Bureau des Longitudes. Avec les notices scientifiques. Paris: Gauthier-Villars, i9oI. (Price, I fr. 5oc.)

The publishers of this annual call special a t ten t ion to the cont r ibut ion of M. A. Cornu on Polyphase Currents, and t ha t of M. I-I. Poincard, on Wireless Telegraphy. The book gives all the statistical data t ha t have made the pre- vious volumes so valuable for reference. W.