POPULAR MISCELLANY. 



717 



of carbon and baked under great heat. Uni- 

 formity in resistance, securing equal con- 

 sumption of current, of surface, and of 

 incandescence, is also indispensable. To 

 " flash " the filament for resistance, it is low- 

 ered into a glass chamber full of a hydrocar- 

 bon gas ; it is heated by an electric current, 

 and the carbon in the gas is deposited on 

 the heated surface. In mounting the fila- 

 ments, the important condition is to obtain a 

 perfect electrical contact or joint between 

 the metal and the carbon, and this is a very 

 delicate point. The soldering is effected by 

 electrically heating the joint in a vessel con- 

 taining a liquid hydrocarbon surrounding, 

 under such condition that the current shall 

 pass through no part of the filament but the 

 joint. Conditions opposite to those of an 

 ordinary light are sought in inserting the 

 filament in the bulb. Not rapid combustion 

 but constant endurance of heating is wanted, 

 and air is carefully removed by exhausting 

 the bulb to one millionth of an atmosphere. 

 In work, during the first two hundred hours 

 of the life of the filament, the electrical re- 

 sistance decreases slightly, and the brilliancy 

 increases ; for the next five hundred hours 

 they are nearly stationary ; after that, resist- 

 ance increases and brilliancy decreases in a 

 progressive ratio. The light is dimmed also 

 by the gradual roughening of the surface of 

 the filament and by the blackening of the 

 glass from the deposition of carbon upon it. 



Economical Plants of Australia. With 

 the exception of timbers, the economic vege- 

 table products of Australia, as presented 

 in Mr. Maiden's book on the Useful Plants 

 of tLat country, are not of extraordinary 

 importance. The northern regions, where 

 the flora is re-enforced by representatives 

 from the Malayan Archipelago and southern 

 Asia, yield most of the plants possessing 

 medicinal properties. The genus Eucalyp- 

 tus, comprising more than one hundred 

 and thirty species, yields excellent timber, 

 kinos, and essential oils. Eucalyptus gunnii 

 yields a sweetish sap which is converted by 

 the settlers into excellent cider. This and 

 manna, from two other species, are proba- 

 bly the only food products derived from 

 eucalyptus trees Oil from Eucalyptus 

 amygdalin and Eucalyptus globulus is pre- 

 pared in Australia and also in Algeria and 



California. In California it is available as 

 a by-product in the manufacture of anti- 

 calcaire preparations for boilers. The aca- 

 cias of Australia, locally known as wattles, 

 are hardly less useful than the gum trees. 

 Immense numbers of them are destroyed for 

 the sake of the bark used in tanning, and 

 the leaves are greedily eaten by stock. By 

 the operation of these two causes they are 

 becoming scarce in some districts, and sys- 

 tematic attempts are now made to plaut 

 them on a large scale. Gum arabic of good 

 quality is yielded by various species of aca- 

 cia, but can not be profitably collected in 

 the present condition of the labor market. 

 Water is obtained by the natives for drink- 

 ing, when springs fail, from the fleshy roots 

 of a tree known botanically as Hakea leu- 

 coptera and from the stem of Vitis hypo- 

 glauca. Very few native Australian trees 

 yield valuable fibers. The native mode of 

 extracting fibers for their fishing-nets is by 

 chewing with their teeth, and by this the 

 teeth are " worn down to a dead level." The 

 best fodder grass of Australia is the plant 

 commonly known as " kangaroo grass." 



Mistakes about Bearings. Mistakes in 

 orientation sometimes of the most puz- 

 zling character are usually the result of 

 some incidental and temporary bewilder- 

 ment, and may under peculiar circumstances 

 overtake any one. Some instances have 

 been cited by Sir Charles Warren in which 

 they are chronic and may afflict even the beet- 

 informed persons. Erroneous conceptions 

 formed by children as to distances and posi- 

 tions may grow up with them undetected till 

 near maturity. Then, when the discovery is 

 made, it is too late to apply any better rem- 

 edy than to recognize the error and make 

 allowance for it when possible. Cases are 

 cited of a person whose ideas of certain 

 parts of London were all inverted ; of an- 

 other, who placed Paris north of London ; 

 of thirty well-informed young men, " about 

 eighteen were under the impression that, 

 while the sun rises in the east, the stars rise 

 in the west, from having learned that the 

 sun has a proper motion among the stars ; 

 and the author believes that there are few 

 educated men who have not grown up with 

 some curious errors with reference to geo- 

 graphical facts, which have bothered them 



