[Illustration] SCIENTIFIC AMERICAN SUPPLEMENT NO. 799 NEW YORK, APRIL 25, 1891 Scientific American Supplement. Vol. XXXI, No. 799. Scientific American established 1845 Scientific American Supplement, $5 a year. Scientific American and Supplement, $7 a year. * * * * * TABLE OF CONTENTS. I. ARCHITECTURE.--Marble and Mosaic.--By T.R. SPENCE.--A paper recently read before the Architectural Association, London, containing valuable suggestions for designers of buildings. The St. Lawrence Hospital for the Insane.--A New York State hospital recently built from designs by the State architect.--Full description.--1 illustration. II. BOTANY.--Lavender and its Varieties.--The history, properties, and technology of this plant.--2 illustrations. III. CHEMISTRY.--A Projecting Apparatus of Precision.--A useful adjunct for the chemist's balance, accelerating the operation of weighing.--1 illustration. Spectrum of the Sun and Elements. Allotropic Forms of Metals. IV. HYDRAULICS.--The Power of Water, or Hydraulics Simplified. --By G.D. HISCOX.--Current wheels for power and raising water. Interesting presentation of this practical portion of the subject. --4 illustrations. V. MECHANICAL ENGINEERING.--Compressed Air Production.-- By WM. L. SAUNDERS.--A Sibley College lecture, giving full elaboration to this important subject.--The various forms of compressors and general features of the service.--18 illustrations. Improved Pneumatic Hammer.--A suspension hammer capable of delivering 500 blows per minute.--8 illustrations. The Thermic Motor of the Future?--A remarkable exposition of the possibilities of the gas engine.--Recent experiments under M. Aime Witz.--2 illustrations. VI. MEDICINE AND HYGIENE.--The Electrical Purification of Sewage and Contaminated Water.--By WM. WEBSTER. VII. NAVAL ENGINEERING.--The New German Dispatch Boat Meteor.--A German built war vessel of great speed.--Her dimensions and rating.--1 illustration. The Raising of the Ulunda.--A remarkable feat.--The raising of a steamship sunk off Nova Scotia.--10 illustrations. VIII. TECHNOLOGY.--Starches for the Finishing of Cotton Fabrics. --Classification of starches, with illustrations of their appearance under the microscope. THE NEW GERMAN DISPATCH BOAT METEOR.