Page:Popular Science Monthly Volume 32.djvu/297

Rh turn, are said to be "often striking, always clever, and generally abominable." The great fault of most modern cameo-cutters is an excessive fondness for detail.

Ground-Water and Health.—Mr. Baldwin Latham, C. E., declares, as the conclusion derived from eleven years of investigation, that there is generally a parallelism between the conditions of health and the volume of ground-water. The years in which there has been a large quantity of ground-water present have invariably been the healthiest years, while those in which there has been a small quantity have invariably been the most unhealthy periods. As a rule, the lowness of the ground-water indicates the future health, and not the state of health at the particular time of lowness; that is, the unhealthy period, as a rule, follows the period of low water, the degree of lowness indicating the intensity of future disease. In some instances an unhealthy period runs concurrently with the period of low water, but in all these cases there is clear evidence that percolation has begun before the unhealthy period comes on. These results, which are confirmed by observations made at Paris, differ from those obtained by Professor Pettenkofer, at Munich, in that he there found typhoid fever and low water concurrent; in all other respects they agree with his. There is also clear evidence, derived from experience in England, that the lowering of the subsoil water by artificial means produces a tendency to the development and dissemination of typhoid fever. It is clear, however, to the author's mind, that groundwater itself has no influence, either for good or evil, upon health, but that the lowness or highness of the water in the ground is the index of conditions which greatly influence the health of all communities. We have periods of abundance of water, and periods of low water, with both healthy and unhealthy conditions. Ground-water has been shown by Professor Pettenkofer to be chemically more impure in periods of high water when the conditions were favorable to health than when there is a low state of the ground-water and a condition unfavorable to health. The records also show that we have periods when rain has started into existence malignant diseases; while, on the other hand, we have similar heavy rainfalls accompanied by a high state of public health. The records clearly point out that it is not one circumstance alone which produces disease, but that there are at least three factors concerned in the matter, especially in the case of typhoid fever, viz.: the elements which produce disease, such as a polluted state of the ground; the conditions which are necessary for the development of disease, such as a period of dryness of the ground in those regions which water usually occupies, combined with a comparatively high degree of temperature; and conditions which will lead to the spread of the disease, such as the probable influence of a storm or rain in driving impurities out of the ground into our water-supplies, or through the instrumentality of ground-air passing into our habitations, and its reception by a population which is in a condition to receive such germs of disease. If any of these conditions is absent, diseases like typhoid do not occur. It has been pointed out by Professor Pettenkofer that in those districts in which the rivers are held up at uniform levels by rains, the conditions are favorable to health, and cholera seldom becomes epidemic. This is corroborated in great measure by the state of health at seaside resorts, which being at the natural outflow for ground-water, and owing to the uniform height of mean tide-level are placed in a condition favorable to health.

Hints in Object-Teaching.—Mrs. Sarah J. Hale, in a little book on "Infant-School Management," gives some excellent precepts for interesting children in subjects of study and making them at home in them. "In every case," she says, "the teacher must bring plenty of illustration to bear upon the lesson. In natural history the real animal, or a picture, should be exhibited, and if possible something that it furnishes us with, as, for instance, the fur of the otter, the shell of the tortoise, the quills of the porcupine. The teacher should also carefully provide herself with pictures of animals which afford strong contrasts to those with which she is dealing, as well as those which bear some general resemblance to it, that she may exercise the discriminative as well