86o 



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 



