��ropular Science Monthly
��liition, and a complete wiring diagram for the entire transmitting and receiving station will be given. The manipulation of the apparatus, the methods of calling and answering and of sending messages, as well as the construction and ijst jf the antenna change-over and the detec- tor-])rotecting switches will he discussed. The remaining instruments needed for the receiver are even easier to construct than the detector and condenser out- lined here. It would be a good plan for the experimenter to complete his tr.insmilter (as described last month) now and ihe apparatus shown in this article, so that he will be all ready to put his station into complete operation soon after the appearance of the next article. It should be remembered that for exchange of messages between two stations it will be necessary to build two of each of the instruments <lescribed, so that each station may be completely equipped aiul thus prepared both for sending and for receiving.
��Caring for Storage-Batteries on Automobiles
WKAK or exhausted battery will cause misfiring in an engine, be-
���Adding luw solution or water to a weak stor- age battery cell to test the specific gravity
cause the current voltage is not sullicient to make a good hot spark jump across the spark-gap. A battery becomes weak, or dc.id, because of some intern. il difcci resulting from short-<ir- 1 iiiling, due to the C(jllecti(jn of
��sediment, destruction of insulation and the bucklingof the plates; or, perhaps too little attention is given to the recharging re(|uirements which vary with the use of the car. It is I)est to anahze the char- acter of the driving before finding fault with the lialtcry to see if a too great demand has been made upon it. A doctor or a city salesman, making many stops, will consume more current than the battery will stand, ilue to the fre- (|uent cranking. Continued use of a car at night will place an added burden on the battery to light the lamjis, which, may e(|ual or exceed the output of thd generator going at the speed one tra\clsl at night. Under these conditions a! battery may be in a completeh' run^i down or dischargetl condition when' tested in the morning. The specific gravity of the electrolyte may drop' below 1,150. One of the chief causes of battery exhaustion is excessive cranking.
The h\-drometer springe is used in the manner illustrated in making tests for sjiecitic gravity. When rehlling the cells with fresh distilled water or putting in a new solution squeeze the bulb, and place the rubber tip in the receptacle containing the solution. The bulb is then released, anil the licpiid is drawn into the glass tube. Insert the tube in the vent hole of the battery, and squeeze the bulb lightK- to eject enough (if the contents to till the cell. Release the l)uli) aiul <|uickh- turn the tube to a horizontal position, to keep the solution from dropping on the upper surface of the battery. Press the bulb to expel the remaining li(|uid, replace the vent plugs ,ind wipe the moisture and dirt from the top of the cell.
To I<>st the specific gra\il\-, dr.iw in enough li(|uid to till the syringe anil hold it toward a light. The floating part will show the density by the graduations.
��Discarded Type-Cases in the Amateur's Shop klStWRDi;!) lyi)e-cases, obtainable from any jirinter, can be put to excellent use in the shop of the amateur mechanic. Such cases may be iise<l for keeping screws, nuts, bolts, washi-rs, etc., w iiere I hey can be easily found. Fasten Iwoor three of them under the work-bench where they will bi' within easy reach.