POPULAR MISCELLANY. 



857 



protected by the branches and foliage of the 

 plant, the more solid earth beneath is also 

 protected from the wash of rain by its mas- 

 sive roots (the author refers to the roots of 

 Simmondsia Californica), while all around 

 erosion goes slowly on, facilitated by the 

 peculiar susceptibility of the soil to wash. 

 Iu the course of time the plant dies is 

 smothered by the drift which nearly covers 

 it, or is destroyed by the annual fires. Thus 

 deprived of its protection, the winds in turn 

 and the rains which fall upon it wear down 

 the top of the loose deposit, and to some 

 extent widen its base. While this is going 

 on the surrounding earth is being continu- 

 ally lowered by the action of water. The 

 wash being greater at the base than at the 

 summit, its effect is to perpetually maintain 

 or increase the prominences. Such is the 

 explanation of these hummocks offered by 

 Dr. Barnes. 



Steadiacssof the Electric Light. In em- 

 ploying the electric light for projection on a 

 screen, two chief points are to be considered, 

 viz., brilliancy of illumination and steadiness 

 of the light. When the source of electricity 

 is sufficient, the first of these ends is easily 

 obtained. The second is not so easy of ac- 

 complishment. The difficulty here met with 

 is pointed out in the " American Journal of 

 Science," by Mr. H. W. Wiley, who also 

 proposes a method of obviating it. The 

 carbons burn away so rapidly that when no 

 mechanism is present to produce alternating 

 currents the electric arc is constantly pass- 

 ing out of the focus. Often, too, Mr. Wiley 

 finds that when the current is quite strong 

 the arc will extend itself momentarily be- 

 tween points as far as a centimetre from 

 the end of the carbons. To prevent this too 

 rapid combustion of the carbons, he coats 

 them with a thin film of copper a plan 

 well known iu France, though seldom tried 

 here. With this coating of copper the car- 

 bons work satisfactorily for a short time ; 

 but soon the film is oxidized, and the com- 

 bustion is as rapid as before. Mr. Wiley 

 therefore protects the copper from oxida- 

 tion by covering the carbons (after copper- 

 plating) with a film of plaster of Paris. 

 After the plaster has set, the edge of the 

 carbon which is to be turned toward the 

 condenser is carefully denuded of its plaster 



covering, which is also cut away till quite 

 thin on the adjacent surfaces. These pre- 

 cautions are taken so that the plaster may 

 not interfere with the radiation of light in 

 the direction of the condenser. The copper 

 surface at the end of the carbon being un- 

 covered, it is fastened in the holder in the 

 usual way. The light now produced is 

 steady and the combustion of the carbon 

 slow. The film of plaster melts gradually 

 as the point is consumed, and thus never 

 interferes with the illumination. The points 

 of both the negative and positive carbons 

 remain blunt, and there is no wasting away 

 of the stem. A carbon prepared in this 

 way will last at least ten times as long as 

 one used in the ordinary way. The chief 

 advantage, however, is found in the com- 

 parative steadiness of the light. 



The Shape of the Earth. There is in 

 England a man named Hampden who be- 

 lieves the earth is flat, and is sorely tried 

 because he can not win all his fellows to 

 this opinion. He is fond of conducting con- 

 troversies on this subject in the public press, 

 and evidently derives great satisfaction from 

 every contest, being a member of that fra- 

 ternity who are " of the same opinion still," 

 however convincing may be the facts and 

 arguments which are adduced against their 

 peculiar ideas. Mr. R. A. Proctor has late- 

 ly found time to engage in a published cor- 

 respondence with this interesting person, 

 and now proposes to settle the matter by 

 an experiment. It appears that, some years 

 ago, Hampden agreed to forfeit a certain 

 sum of money if the result of a similar ex- 

 periment should prove to be adverse to his 

 opinion. He lost the money. To this ex- 

 periment Mr. Proctor alludes in the open- 

 ing sentence of his challenge, which is as 

 follows : " In the Bedford Canal experi- 

 ment, the result of which cost Mr. Hamp- 

 den so much loss and annoyance, he dis- 

 trusted the evidence of the referee's eyes, 

 and considered also that there should have 

 been three boats in line, one at each end 

 and one in the middle of the long distance. 

 Now, as nothing would be easier than to 

 photograph three boats so arranged on a 

 clear, quiet day, and as the collodion-film 

 can neither be deceived nor lie, I can not un- 

 derstand why he should not try that simple 



