Motion Picture News (Mar-Apr 1923)

1712 Motion Picture News Simplified Electricity for Projectionists (Continued from page 1710) voltages buck the terminal voltage they must all be acting in the opposite direction to it and hence have the opposite sign which is minus. Now Kirehoffs Law says that the sum of all these voltages, with proper regard to their respective signs, is equal to zero. This can be expressed as an equation as follows : (1) (-In) + (-Ir2) + (-I^) + (+E,) = O and since e = ir, ( — e.) + ( -*)+( -h?0 + (+E.) = 0 removing the brackets we have — e. — e. — e. + Et = 0 adding — ei — e, — es to each member E, = e» + e, + e* In order to determine the final sign when the voltage is enclosed in brackets the following rules can be used : — [ — e] = + e = e + [-e]=-e — [+e] =-e + [ +e] = + e = e Now the first equation (marked (1) ) can also be written E, = Ir. + Ir, + Ira Since I is present in each term of the right member we can factor as follows (the word factor means to take the same quantity from each term) : E, = I + » + Now (n + r»-+ r3) is the total resistance, R, of the local circuit so we can also say E, = IR remembering that R (total resistance) = (r. + r. + ft). Thus in order to find the current flowing in Fig. 23 when n = 2 ohms, n = 4 ohms and r3 = 6 ohms and when E, = 120 volts, we proceed as follows: Et = I (n + ft+ft) divide each side by (r. + r2 + ft) _^ =I (ft + v, + ft) 120 _ (2 + 4 + 6) -L I = 10 amperes Since this is a series circuit (all the resistance are in series, one behind the other) the same current flows through each resistance so that the drop across each is as follows: e, = In = 10 X 2 = 20 volts es = Ir, = 10 X 4 = 40 volts e3 = Ira = 10 X 6 = 60 volts and since E, = ei + e, + e= E, = 20 + 40 + 60 E = 120 volts also, in order to check Kirehoffs Law — ei — e> — es + Et = O —20 — 10 —60 + 120 = 0 TABLE IV. Electrical Properties of Copper Wire. Current Capacity ill , — Amperes — , Re--i-t Rubber Area in ance C( vered Other B & Diameter Circular in Ohms In In S. in Mills Mills per 1000 sula sula No. at 20° C at 20° C feet at 20° C tion tion 0000 460.0 211,600 0.04901 225 325 000 409.6 167,800 0.06180 175 275 00 364.8 133,100 0.07793 150 225 0 324.9 105,500 0.09827 125 200 1 289.3 83,690 0.1239 100 150 2 257.6 66,370 0.1563 90 125 3 229.4 52,640 0.1970 80 100 4 204.3 41,740 0.2485 70 90 181.9 33,100 0.3133 55 80 6 162.0 26,250 0.3951 50 70 8 128.5 16,570 0.6282 35 50 10 101.9 10,380 0.9989 25 30 12 80.8 6,530 1.5880 20 25 14 64.1 4,107 2.525 15 20 16 50.8 2,583 4.016 6 10 18 40.3 1,624 6.385 3 5 Other Insulation " means such insulation as asbestos covered wire which is not so readily affected by heat a* rubber. Big Demand for SlideOGraph Reported The Standard Slide Corporation of New York City reports exceptionally heavy sales on the new " Slide-o-Graph," the automatic advertising machine for theatre lobbies. This apparatus permits the showing of the most interesting scene of each coming feature and also vaudeville acts in the front of the lobby, thus keeping all those who pass the theatre informed concerning the daily program and feature attractions at an exceptionally low advertising cost to the exhibitor. " Slide-oGraphs " use attractively colored slides and are effective both day and night. Reynolds Electric Publishes Bulletin The Reynolds Electric Company has recently published a bulletin containing the care and maintenance for electric flashes. This bulletin should i^rove of help to those operating this type of equipment. — Agard. Predict J. J. Harners Return to Industry Many expressions of hope that the Sun Light Arc Corporation which went into bankruptcy early in the year, would resume business activities, have reached J. Justice Harmer, president of the company, and thpse expressions have laid emphasis upon the belief that Mr. Harmer, who made the Sun Light arc the factor it is in this industry, would be especially welcome as the head of a stronger and more solidly established Sun Light Are Corporation. The Sun Light Arc Corporation was organized with Mr. Harmer as president in 1918, and found itself confronted with many adverse business conditions, due to the general situation of the country at that time. The Sun Light arc has been of vital importance for the economic production of pictures. Westinghouse Develops New Type of Heater A new type of heater, known as the Type MP heater, to be used especially in ticket booths, has been designed by the Westinghouse Electric and Manufacturing Company. The heater, which is 20 inches in length, is easy to install and requires little space as it can be attached to the side of the booth by screws. The resistance units are mounted inside and the heater is of all-steel fireproof construction, making it safe and reliable. It will serve also as a foot rest for the person occupying the booth and the danger of damage to footwear is eliminated by reason of the foot rest on the heater being sufficiently removed from the cover protecting the resistance units by an air space. A three-heat snap switch also insures the right amount of heat. The heaters are of black Japan finish and are supplied for 110 and 220 volt circuits. Davidson of Norwich, Ct. , to Build Indications are that AVillimantic, Conn., is to have another motion picture house, as a result of the Abe Davidson of Norwich, Conn., buying from Joseph Giraca a lot on Main street, in the former city, having a frontage of 40 and depth of 169 feet. For some time, Mr. Davidson has been looking over available sites in this city, with the admitted intention of building another screen-program playhouse. Blank for New League Members Member's Name New applicants when sending in blanks for membership in the NATIONAL ANTI-MISFRAME LEAGUE PLEDGE J S a motion picture projectionist who has the interest of his profession at heart and is willing to assist in eliminating some of the evils practised in the projectionroom, I promise that I will to the best of my ability return films to the exchange in reasonably good condition, according to conditions of film when received. Furthermore. I will when it becomes necessary remedy misframes. bad patches, etc., that may be in the film which I receive and in this way co-operate with my brother projectionists and give greater pleasure to those who make up the motton picture audience by showing films that are free from such defects. I also promise that I will not make punch marks in film, and when film is received by me, with punch holes, I will notify the exchange to that effect so that they may use their efforts to correct this evil. N. A. M. please enclose twenty-five cents for a membership button