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POPULAR SCIENCE REVIEW. 
an instrument which its inventor, Prof. Alfred W. Mayer, terms the ‘ Topo- 
phone,’ or Sound-place. 1 It consists of a vertical rod passing through the 
roof of the deck cahin, hearing on its upper end a horizontal bar, carrying 
two adjustable resonators, below which a pointer is set at right angles with 
the bar. Rubber tubes from the resonators pass through the roof of the 
cabin, and unite in a single pipe connected with a pair of ear-tubes. The 
vertical rod is turned, by means of a handle, in any direction. The first step 
is to tune the resonators accurately to the pitch of the sound under observa- 
tion, and the second to fix them ‘ at a distance from each other somewhat 
less than the length of wave of that sound ; next, by turning the handle to 
bring them simultaneously on the wave-surface, when, as they both receive 
at the same instant the same phase of vibration on the planes of their mouths, 
it will result that, if the connecting tubes be of the same length, the sound- 
pulses acting together will be reinforced to the ear ; but if the tubes differ in 
length by one half the wave-length of the sound, the pulses will oppose and 
neutralize each other. At this moment the horizontal bar is a chord in the 
spherical wave-surface, of which the distant fog-horn is the centre, and the 
pointer represents a radius directed to the place from which the sound 
emanates.’ This seems a pretty and useful little problem to set to a skipper 
in a gale and a fog, with an unknown danger-signal hardly audible in the 
offing. It is just possible that he might be better employed on deck. 
Dynamo-electric Machines for Telegraphic Purposes, are described in a 
late number of the Scientific American. They are intended to replace 14,800 
gravity battery elements, and 4600 bichromate of potash cells. The machines 
are on Siemens’s system, connected in series with their field-magnets excited 
by a current from a single Siemens machine. One commutator-brush of a 
machine is connected with the brush of opposite polarity in the next, and so 
on, so that a current of any desired potential may be had from the different 
machines in the series. The E. M. F. in the first being 50 volts, the second 
will be 100, and the third 150. A patent to this effect was taken out by 
Mr. II. Wylde in 1878 in this country. Dr. Schwendler, Electrician to the 
Indian Government, finds the dynamo-electric current better for telegraphic 
purposes than those from batteries. A signal current can be obtained from 
that maintaining a powerful light by derivation without perceptibly dimin- 
ishing the lighting power. 
Atmospheric Polarization and the influence of Terrestrial Magnetism on 
the Atmosphere form the subject of a memoir in the Annales de Chimie et de 
Physique, by Henri Becquerel. First observed by Arago in 1809, it was 
further worked out by Babinet, Brewster, Bernard, Liais and Rubenson. 
If the light emitted by the atmosphere in the sun’s vertical plane be analysed 
at an hour when the luminary is at a small elevation above the horizon, it is 
found to be faintly polarized in his neighbourhood, the polarization increasing 
towards the zenith. The maximum occurs at an angle of 90° from the sun, 
falling again to zero at a point named Arago’s neutral point. Up to this the 
plane of polarization is vertical, below it it is horizontal. At sunrise and 
sunset, the neutral point is from 20° to 30° above the horizon. Babinet found 
a second above the sun, and Brewster a third at about the same distance 
below. There seem to be other secondary neutral points related to those 
above named, and discoverable in certain states of the atmosphere. 
