Page:Popular Science Monthly Volume 32.djvu/440

426 often cut and polished and palmed off as diamonds; but this material is costly. A composition for rubies is made of five hundred parts of strass—a specially manufactured glass—twenty parts of glass of antimony, and a half-part each of purple of Cassias and gold. Mock pearls are some-times very deceptive in appearance, but they can usually be detected by comparison with the real gem, by their brittleness, or by the clumsy and blunt-edged appearance of the drill-holes, which are usually perfect in the real pearls. The scales of a small fish known as the bleak have been used in the formation of false pearls; but as it requires some eighteen thousand of these fish to provide one-pound weight of the pearl-making material, the manufacture is not likely to become extensive.

Preventable Loss in Agriculture.—In a British Association paper on this subject, Professor W. Freame first described the uncontrollable losses which were chiefly such as were determined by meteorological conditions. These, if they could not be anticipated, might to some extent be mitigated by acting upon the recorded practice which had been found most beneficial in similar cases in previous years. Hence the value of such records. Controllable losses were such as might reasonably be anticipated, and therefore provided against, and should be in a very high degree, although not absolutely, preventable. The toleration of such preventable losses might be attributed partly to ignorance, partly to indifference, and partly to empiricism. First among the sources of preventable loss was the imperfect working of the soil, which was a common cause of poor crops in the immediate future and of worse trouble farther on. Another source was the use of bad seed. No greater folly could be conceived than that of introducing upon the land by means of purchased seeds the seeds of weeds and parasites. The most objectionable rubbish was sometimes sown, and heavy expenses were in consequence subsequently incurred. A third source was the encouragement of weeds, of which the most common species were grown at immense cost to the farmer. They robbed him just as much as a pickpocket did who stole his purse. His object was, or should be, to concentrate all the capacities of the soil upon the production of useful crops; every weed that was grown detracted from this purpose. Ignorance of the properties and affinities of weeds was just as deplorable. Some—the cruciferous weeds, for example—harbored and encouraged insect pests till the cruciferous crop they were waiting for was ready to be devoured and destroyed by them. Another source of loss was the deterioration of grasslands. There were in the British Islands nearly thirty-three million acres of permanent or temporary grass land, which was equivalent to three sevenths of the entire area. Yet. as to the nature of the herbage growing upon this enormous area, ninety-nine farmers out of one hundred were in entire ignorance. A fifth source was from pests. The maintenance of insect-thieves sometimes constituted a severe drain upon farming capital. Yet in no part of his education was the farmer called upon to familiarize himself with the habits of these creatures. Of fungi pests, his knowledge was, if it were possible, even less. Other sources were diseases of livestock, some of which were preventable and some greatly reduced, while others stood in need of further investigation; and injudicious expenditure. Among the most practicable remedies for these preventable losses, and a means, therefore, for making agriculture a more profitable occupation, was the extension of sound technical instruction in agriculture.

Photography as an Aid to Astronomy.—Mr. A. A. Common believes that some astronomical objects can be studied to better advantage in photographs than in themselves. The brain can not always take in the perceptions of the eye fast enough, and the eye is not sensitive to images whose brightness falls below a certain limit. In photography, a prolonged exposure may be made to compensate for deficiency in luminous power; and the sensitive plate being competent to respond to quicker vibrations than the eye, it is possible to obtain photographs of celestial objects radiating light which the eye is not adapted to receive. While the moon has received much attention, the photographs of it taken by Rutherford, twenty years ago, have not been