Popular Science Monthhi 



03 1 



Tcrminols - 



Oie'.ednc 



electricity it has on either plate, divided 

 by the potential difference between the 

 plates. A condenser would, therefore, 

 have a capacity of unity in the practical 

 system of units if it would hold a quantity 

 of one coulomb, 

 (the quantity of 

 electricity trans- 

 ferred when a cur- 

 rent of one am- 

 pere flows steadily 

 for one second), 

 at a difference of 

 potential of one 

 volt. Such a ca- 

 pacity is called a 

 farad. This unit 

 represents, how^- 



ever, an enormous capacity as compared 

 to those met with in practice, so that 

 it is usual to express capacities in micro- 

 farads, (m.f.). Thus, one m.f. = 0.000001 

 farad = farad ^ 10*^ = farad x 10"^ 

 But, whenever the general equation is 

 used, the capacity must always be re- 

 duced to farads. 



Tig 6 



A number of plates 

 made up into sets 



Securing Wood or Metal Molding to 

 Plaster Walls 



THE electrician will find, when putting 

 up wood or metal molding, that by 

 drilling two holes, A, 1 in. apart, instead of 

 one hole, every 3 ft., that not only will 

 time be saved but the molding Vvdll be 

 more secure. The reason for this is that 

 if the hole B was used and the screw went 

 through the plaster between the laths, it 



Two holes drilled close together into the 

 molding hastens the work in putting it up 



would be a simple matter to put a screw 

 in hole C and to strike a lathe into which 

 the screw could easily be fastened. 



Now We Reach the Philippines 

 Directly by Wireless 



THE last link in a long chain of wire- 

 less stations, reaching from Arling- 

 ton, near Washington, to the Philippine 

 Islands, was recently forged. Cavite, this 

 latest station, situated near Manila, has 

 been building for some time. At its 

 opening Admiral Knight, commander of 

 the Asiatic fleet, sent a message of greeting 

 to Secretary Daniels. In his reply 

 the Secretary commented upon the ease 

 with which our warships in Asiatic waters 

 can now be reached. The chain of sta- 

 tions consists of Arlington, Darien, San 

 Diego, Pearl Harbor, and Cavite. 



A Small Storage Battery Made With 

 a Sponge 



A STORAGE battery can be made 

 from two lead plates and an old 

 sponge, that will give good service for 

 lighting a small lamp or running small 

 motors. 



The battery is 

 made with a one- 

 pint glass fruit jar. 



A, two lead plates 



B, Y?, in. in diame- 

 ter and as long as 

 the jar, are bent to 

 set opposite each 

 other, each cover- 

 ing one-fourth the 

 inside circumference 

 of jar, A large 

 coarse sponge C is 

 obtained which 

 must be thoroughly 

 cleaned and dried. 

 Then obtain a piece 



of lead, and with a coarse file cut off 

 enough filings to fill every pore in the 

 sponge. When this is done, sprinkle the 

 filings on the sponge which is in the jar 

 between the plates. Be careful to keep 

 the filings from falling out of the pores. 

 The sponge must fit tightly against the 

 walls of the jar to hold the filings in. 

 Next fill the jar with one part sulphuric 

 acid to seven parts of distilled water. 



If this battery is charged in series with 

 a 16 C. P. lamp on 110 volt D. C. line it 

 will give 2 volts and 14 ampere hours. — 

 William Harrier. 



A 16 c. p. lamp must 

 be used while charging 



