Tyndall thought that the blue color of water had a similar cause as the blue color of the air, being blue by reflected light and red by transmitted light. W. Spring has recently communicated to the Belgian Academy the results of his investigations upon the color of water. He proved that perfectly pure water in a tube 10 meters long had a distinctly blue color, while it ought, according to Tyndall, to look red. Spring also showed that water in which carbonate of lime, silica, clay, and salts were suspended in a fine state of division offered a resistance to the passage of light that was not inconsiderable. Since the red and violet light of the spectrum are much more feeble than the yellow, the former will be completely absorbed, while the latter passes through, producing, with the blue of the water itself, different shades of green. * * * * * There is to be held in Paris this year, from the 1st to the 22d of July, an insect exhibition, organized by the Central Society of Agriculture and Insectology. It will include (1) useful insects; (2) their products, raw, and in the first transformations; (3) apparatus and instruments used in the preparation of these products; (4) injurious insects and the various processes for destroying them; (5) everything relating to insectology. * * * * * A catalogue, containing brief notices of many important scientific papers heretofore published in the SUPPLEMENT, may be had gratis at this office. * * * * * THE SCIENTIFIC AMERICAN SUPPLEMENT. PUBLISHED WEEKLY. TERMS OF SUBSCRIPTION, $5 A YEAR. Sent by mail, postage prepaid, to subscribers in any part of the United States or Canada. Six dollars a year, sent, prepaid, to any foreign country. All the back numbers of THE SUPPLEMENT, from the commencement, January 1, 1876, can be had. Price, 10 cents each. All the back volumes of THE SUPPLEMENT can likewise be supplied. Two volumes are issued yearly. Price of each volume, $2.50, stitched in paper, or $3.50, bound in stiff covers. COMBINED RATES--One copy of SCIENTIFIC AMERICAN and one copy of SCIENTIFIC AMERICAN SUPPLEMENT, one year, postpaid, $7.00. A liberal discount to booksellers, news agents, and canvassers. MUNN & CO., PUBLISHERS, 261 BROADWAY, NEW YORK, N. Y. * * * * * PATENTS. In connection with the SCIENTIFIC AMERICAN, Messrs. MUNN & Co. are Solicitors of American and Foreign Patents, have had 38 years' experience, and now have the largest establishment in the world. Patents are obtained on the best terms. A special notice is made in the SCIENTIFIC AMERICAN of all Inventions patented through this Agency, with the name and residence of the Patentee. By the immense circulation thus given, public attention is directed to the merits of the new patent, and sales or introduction often easily effected.