Besides investigating other phenomena connected with a vacuum, he constructed an electrical machine which depended on the excitation of a rotating ball of sulphur; and he made successful researches in astronomy, predicting the periodicity of the return of comets.
Manson showed in 1881 that the larvae (Microfilariae) were not at all times present in the blood, but that their appearance had a certain periodicity, and the larvae of F.
They, however, show no periodicity, and are found continuously both by day and by night; and their larval forms are termed Microfilaria perstans.
The conditions permit of the circulation of the alternating currents of low periodicity, which are used for operating the bells, but in respect of the battery the circuit is open until the subscriber lifts the receiver, when the hook switch, thus released, joins the transmitter with one winding of an induction coil in series across the circuit.
In this case there is approximate periodicity in the half interval, but complete periodicity only after the whole interval.