��THE POPULAR SCIENCE MONTHLY.
��light and dust may not affect her carpets and bric-d-brac, perfectly unmindful that the care she bestows to protect these things is fraught with risk to the health and life of a son or daughter. She does not know, nor has she taken the pains to learn, nor has any one undertaken to instruct her, that the bacillus of such diseases as typhoid fever, diphtheria, phthisis, and most diseases which have a specific germ, can not exist and hold their identity in solar light and air, which, as has been demonstrated by Koch, kills them in from a few moments to a few hours, whereby no room is left for doubt that, by the construction of our houses and by the studied exclusion of light and air, we do most for the retention of these disease- germs, and at the same time contribute to the preservation of their vitality.
Earliest Use of the Mariner's Compass. —
The history of the discovery of the mariner's compass by the Chinese is lost in their an- tiquities. It is supposed to have been acci- dental, in a province where there is much magnetic iron ore, from the observation that a needle made from that ore, when by any means it was caused to float on water, as- sumed a north and south direction. The earliest author who mentioned the " south- pointing needle " lived in the fourth century B, c. It probably came into use when the professors of fung shue or geomancy began to study landscape, about the eighth century of the Christian era. Their instrument was made of hard wood, about a foot wide, with a small well in the middle, in which a mag-netized needle floated in water. On the compass were inscribed several concentric circles, as on the wooden horizons of our globes. They embraced the twelve double horns, the ten denary symbols, eight dia- grams, and other marks. This compass was used in preparing a geomantic diagram of any spot where a house or tomb was to be constructed, so that the construction might not be upon an unlucky site, or planned in an unlucky manner. At the same time there was living a Chinese who had studied Hin- doo astronomy, and was the imperial astrono- mer and also a Buddhist priest. He noticed that the needle did not point exactly north, but varied by 2° 5'. The variation went on increasing till a century later, or the ninth
��century. Shenkwa, writing in the eleventh century, mentions that any iron needle could be given polarity by rubbing it on a piece of loadstone. After this, in 1122, an ambassa- dor to Corea described the use of the float- ing needle on board ship while he made the voyage. This is the earliest instance, by more than a century, of the use of the mari- ner's compass on board ship found in any book. At that time the needle was floated in water, supported by a piece of wood ; but in the Ming dynasty some Japanese junks engaged in piracy were captured by Chinese, in which the needle of the compass was dry and raised upon a pivot. The Japanese hud i learned this from the Portuguese. The Chinese from that time also hung their compass-needles on a pivot.
An American Exhibition in Spain. — The
Spanish Government is preparing to estab- lish at Madrid, in honor of the fourth cen- tennial of the discovery of America, an ex- hibition of every kind of American objects, so constituted as to give an idea of the civil- izations of the American world, both previ- ous to and coeval with the epoch of the dis- covery and the European conquests. For this purpose the commission solicits contri- butions of American objects illustrating prehistoric America — plans, models, and re- productions of drawings of cave dwellings, megalithic monuments, and lake dwellings, and of objects of all kinds of the palfeolithic and neolithic ages, and of the bronze and copper ages. Of the historical period are wanted models or representations of build- ings and architectural fragments, specimens of polychromatic architecture, representa- tions of restored monuments, and works of fine art of every kind. In the department of industrial arts, etc., clothing and adornments of aboriginal uncivilized or only partly civil- ized Indians are asked for, implements of war of wood, copper, bronze, and iron ; gold, silver, bone, and ivory jewels, necklaces, ear- rings, bracelets, etc. ; pottery, household utensils, and furniture; tissues and textiles from which they are made; apparatus for manufacturing purposes ; articles used in transportation ; native documents ; Indian portraits and effigies ; models of Indian dwellings, crania, etc. Old maps, articles relating to cartography, whatever relates to