. Nature . to wait untilthe other drum has caught it up. Whenthe transmitting drum has completed itsturn, a fleeting contact comes into play,a reverse current is sent to the receivinginstrument; this is led into a polarisedrelay, which actuates an electromagnet,and this magnet removes the , however much one drum gets out of step withthe other, the fault is limited to each revolution, and bothdrums must always start off in unison for each new revolu-tion. I have found that where each operator endeavoursto keep his motor running uniformly by regulating theresistance according to the fl
. Nature . to wait untilthe other drum has caught it up. Whenthe transmitting drum has completed itsturn, a fleeting contact comes into play,a reverse current is sent to the receivinginstrument; this is led into a polarisedrelay, which actuates an electromagnet,and this magnet removes the , however much one drum gets out of step withthe other, the fault is limited to each revolution, and bothdrums must always start off in unison for each new revolu-tion. I have found that where each operator endeavoursto keep his motor running uniformly by regulating theresistance according to the fluctuations recorded by thefrequency meter, the personal element makes itself visiblein the results; straight lines appear wavy, and thesynchronism is not at all good. I therefore tried verycarefully calibrating the motors by timing first, and thenarranged that, once started, the motors should not betouched; the gain in speed of each is approximately thesame if both motors are run from secondary batteries of. the same ampere-hour capacity, and in this way we haveobtained the most perfect results as regards synchronisa-tion. The great advantage of this process is that the wholeoperation is in full view, whereas with systems in whichthe received picture is obtained on a photographic filmone has to develop such film before it is possible to dis-cover whether anything is wrong. With the receiverdescribed, the operator keeps his hand on the sliding con-tact of the resistances, and merely adjusts their positionduring the first two or three seconds, according to thecondition of the electrolytic marks, whether crisp andconcise or not. The transmitting cylinder can be used asthe receiving cylinder, and the apparatus is thus reducedto the limits of simplicitv. Towards the end of last year I designed a portable NO. 2129, VOL. 84] August i8, 1910] NATURE machine, two of which Mr. Sanger-Shepherd has justcompleted, embodying in them a number of improvementsof his own, and these machines
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