Decembek 1, 1897.] 



KNOWLEDGE. 



293 



Vediilia cardinalis (the imported Ladybird 

 enemj of the W'liite Scale) ; a, Ladybird Larva* 

 feetling on Female Scale ; b, Pupa, and c. Adult 

 Ladybird ; d. Orange Twig showing Scale and 

 Ladybirds, natural size. 



The most destructive insect enemies of fruits in Call- ] 

 fomia are undoubtedly the scale insects (CoceWte). Many \ 

 methods are employed by fruit growers in California to 

 control the ravages of injurious insects of this and other 

 kinds, as may be seen from a paper in the " Year Book " of 

 the United States Department of Agriculture. Bitt one of 

 the most satisfactory is the importation of natural enemies 

 of the noxious species. A few years ago the very existence 

 of citrus culture in California was threatened in consequence 



of the attacks of 

 the white scale 

 [Icei/ra purchnsi). 

 A ladybird 

 enemy of the 

 pest, Veil all a 

 cardinalis, was, 

 however, intro- 

 duced into the 

 State from Aus- 

 tralia, and it 

 did its preda- 

 tory work so 

 thoroughly that 

 the white scale is 

 no longer an im- 

 portant injurious 

 insect. The 

 accompanying 

 figure, repro- 

 duced from the 

 paper to which 

 reference has 

 been made, shows this ladybird and its larvse. This 

 noteworthy instance of the almost total eradication of an 

 injurious insect by the importation of its predaceous enemy 

 has given great confidence in the natural means of con- 

 trolling insects. Enormous numbers of difierent varieties 

 of ladybirds have been introduced, and one of them, the 

 little beetle Bliizohivs ventralis, has entirely exterminated 

 the black scale insect (Lecanitim olece) from several badly 

 infested orchards. There can be no doubt about the 

 beneficial influence of these beetles at present, and the 

 restilts furnish a striking instance of the industrial appli- 

 cation of the facts of entomology. 



^'*~t 



A school of ethics and social philosophy has just been 

 formed, the general committee including the Master of 

 Balliol, Mr. LesUe Stephen, Prof. Sully, and others. 

 Special attention will be given to the bearing of recent 

 psychology upon problems of education, and to the 

 philosophical analysis of the structure of society and the 

 functions of its organs. Lecture rooms have been secured 

 at the new Passmore Edwards settlement in Tavistock 

 Place, W.C, and the secretary, pro tern., is Mr. J. H. 

 Muirhead, 30, Aynhoe Road, West Kensington. 



!-•-• 



A very useful volume of classified and illustrated abridg- 

 ments of specifications relating to philosophical instruments, 

 1884-88, has just been issued by the Comptroller of Her 

 Majesty's Patent Oflice, and we understand that similar 

 volumes on other subjects and groups of subjects are 

 obtainable. To those persons requiring information as to 

 what is already protected in the way of invention by letters 

 patent these volumes must be a real boon. The laborious 

 process of searching through the records of the Patent 

 Office is by this means reduced to something Uke ten per 

 cent, of what it used to be, a concise and imderstandable 

 short paragraph, as a rule, taking the place of many whole 

 pages in the full specification. 



A trial journey in a motor car over a distance of a 

 hundred miles on- the Carlisle road has been accomplished 

 in eight and a half hours, including stoppages. The 

 amount of fuel consumed was five gallons, the total cost, 

 including lubricating oil, being 4s. lOd. for the hundred 

 miles. Three passengers were carried, and the net cost 

 per passenger was therefore about Is. 8d. for the journey. 

 — *■•■* — 



The experiment of floating a steel needle upon water is 



an old one ; nevertheless it is easier described than success- 

 fally performed. It is often stated that the needle must 

 be greased, but this is a mistake, for to float a needle 

 upon water its surface should be quite clean. Shortly 

 before his recent death, it occurred to Prof. Alfred M. 

 Mayer that by floating a disc or ring of metal with a 

 chemically clean surface, and gradually weighting it until 

 it broke through the surface of the liquid, the surface 

 tension cotUd be measured. The 

 discs experimented upon were made 

 of aluminium ; they were one- 

 twenty-fifth of an inch thick, and 

 from two to three inches in diameter. 

 Discs of these dimensions could not 

 only be made to float upon water, 

 but a small extra weight had to be 

 added to them in order to make 

 them sink, and the water surface 

 was depressed by about one-tenth 

 of an inch before the tliscs broke 

 , through it. To determine the weight 

 necessary before a ring of metal 

 breaks through a liquid surface, an 

 ; arrangement of the form shown in 

 the accompanying figure was used. 

 Prof. Mayer found that if a floating 

 ring of this kind, formed of wire 

 about one-twenty-fifth of an inch in 

 diameter, be gradually loaded by 



pouring fine sand into the cup carried by the ring, it sinks 

 deeper and deeper into the depressed surface of the water 

 till it has reached a depth of one-tenth of an inch, when it 

 suddenly breaks through the surface and sinks, as in the 

 case of the discs. Using the data thus obtained, the surface 

 tension of the water can be calculated. It was found that 

 all metals, with clean surfaces, from platinum, having a 

 density of 21-o, to magnesium of a density 1-7, float on 

 water. The reason appears to be that a film of air coats 

 the surfaces of metals and keeps them from touching the 



water. — '^ , " . , 



In a recent issue of the Statist there is an article on 

 " The World's Gold Production since 1850." A chart is 

 given showing the variations in production in each year 

 from 1851 to 1896. For the latter year the production by 

 fields was as follows ;— United States, £10,000,000 ; 

 Australasia, £8,988,000 ; Transvaal, £8,604,000; Indian, 

 £.5 911,000; Russia and other countries, £10,697,000— or 

 a total 'of £45,000,000. The grand aggregate of the gold 

 production since 1850, inclusive, is, m round figures, 

 £1,163,000,000, or approxunately 300,000,000 ounces of 



gold. — ''•"■ — 



Expectations as regards the Leonids have so far been 

 anything but realized. Watchers in many parts have, 

 so to speak, cast their nets and caught nothing. Those 

 who were fortified with cameras and eagerly scanned the 

 heavens about the time of the expected display, found 

 meteor and shooting-star catching quite an unexcitmg 



recreation. — '^ — „ . , ■ ^ i 



M. Czernich, the well-known Russian chemist, haa 

 exaruined two minerals from the Caucasus. One of them 



