June io, I920] 



NATURE 



467 



I 



bv the definite tidal oscillations of the Atlantic Ocean 

 and the North Sea at the two ends of the Channel ; 

 this view had been contested by Borgen, but the 

 consequences of the view were misinterpreted by the 

 latter. Dr. Defant shows that not only the co-tidal 

 lines and tidal ranges, but also the phase and sf>eed 

 of the tidal currents in the Channel, can be explained 

 on the basis of .\iry's ideas, talcing surface friction at 

 the channel-bed into account, and also the rotation 

 of the earth. He finds that the latter affords an ex- 

 planation of why the tidal rang^e on the French coast of 

 the Channel is greater than that on the English coast. 

 For the sections of the Channel near the east opening 

 into the North Sea the calculations cannot be executed 

 with the accuracy eli^ewhere obtained, owing to the 

 approximation of the ocean-tidal period to the free 

 period of lateral oscillation across this broad part of 

 the Channel. But even here the chief features can be 

 derived by interpolation, and throughout the remainder 

 of the Channel all the important features of the com- 

 plex Channel tides receive satisfactory theoretical 



< xplanation. 



The paper read by Gen. Squier to the U.S. National 

 Academy on April 27 on " Multiplex Telephony and 

 Teleg-raphy over Open-circuit Bare Wires Laid in 

 the Earth or .Sea " has excited great interest amongst 

 radio-telegraphists, who find it difficult to make out 

 whether we are on the eve of important developments 

 or not. Gen. Squier has established communication 

 for a distance of three-quarters of a mile over the 

 Potomac River by means of a bare No. 12 phosphor- 

 bronze wire laid directly in the water. The*trans- 

 mitter consisted of an electron tube oscillator, which 

 produced a current of about 270 milliamperes at a 

 frequency of 600,000. At the receiving end of the 

 line an electron tube and a six-stage amplifier were 

 used without any earth connection. With this 

 arrangement good tuning could be obtained at either 

 end of the line, and satisfactory telegraphic and tele- 

 ])honic transmissions secured by means of ■ the bare 

 wire immersed in fresh-water. In another experi- 

 ment telegraphic and telephonic transmission were 

 obtained between two stations three-quarters of a 

 mile apart by means of a No. 16 copper wire buried 

 in the earth to a depth of about 8 in. It will be 

 seen that if the method develops satisfactorily it will 

 have commercial possibilities. The best .\tlantic 



< able cannot operate at a frequency greater than 10 per 

 x'cond, and 80 volts is the highest voltage that can 

 )<! applied to work it. There is scope, therefore, for 



<ievelopment in submarine telegraphy. Gen. Squier 

 suggests that experiments should be made with bare 

 wires in sea-w'ater to determine what arrangement 

 will give the best results. He points out that with 

 this method there will be no distortion of the signals, 

 and so there is no limit to the distance of trans- 

 mission, and the receiving apparatus will be com- 

 paratively simple. It is also possible to transmit 

 simultaneously several signals, both telephonic and 

 telegraphic, over the same wire by using different 

 frequencies. The method is an attractive one, and 

 seems to have arrived at the stage where commercial 

 research can u.sefully be started. 

 NO. 2641, VOL. 105] 



Our Astronomical Column. 



Pnor<)c;K.\rns ok thk Bkorskn-Metcalf Comet. — 

 The Astrophysical Journal for March contains some 

 photographs of this comet taken by Prof. Barnard on 

 1919 October 5, 6, 20, and 22. The tail is shown as 

 fully 6° long, composed of several narrow straight 

 streamers forming a fan. They radiate from a point 

 somewhat behind the centre of the head. About 

 October 20 the comet discarded its tail, and fonned a 

 new one inclined 12° to the old. Prof. Barnard notes 

 that similar phenomena have been observed in 

 Borrelly's comet, 1903 July 24, in Morehouse's comet 

 on several dates in 1908, and in Hallev's comet on 

 19 10 June 6 (probably also in April), 



In each case the new tail appears to move out 

 faster than the rear portion of the old tail. ProL 

 Barnard conjectures that the latter is formed of larger 

 particles, the motion of which would be slower. 



He has combined successive cometary photographs 

 in the stereoscope in the endeavour to determine the 

 configuration of the tail in three dimensions. Care is, 

 of course, required to distinguish true stereoscopic 

 effects from spurious ones. It is stated that the 

 tail of Morehouse's comet on October 15, 1908, re- 

 sembled "part of an open sack, or a partlv opened 

 scroll." 



The Planetary Families of Comets. —The report 

 of the nineteenth meeting of the American Astro- 

 nomical Society contains a paper on this subject bv 

 Prof, H. N. Russell. He notes that the orbits of the 

 six comets of the Neptune group all pass considerablv 

 closer to the orbits of Jupiter and Saturn than they 

 do to that of Neptune. His first conclusion was that 

 these comets had been captured not by Neptune, but 

 by Jupiter. He analysed the orbits of the periodic 

 comets with the following result : — 



Thirty-six comets on his list have periods of less 

 than ten years. The orbits of all these, except 

 Encke's, pass within 065 of Jupiter's orbit, while 

 seventeen of them pass within 0-15 of it. 



Thirty-one comets have periods between ten and 

 one thousand years. Of these, seven pass within 05 

 of Jupiter's orbit, five within the same distance from 

 Saturn's orbit, and two within this distance from 

 Uranus 's orbit, the nearest approach to Neptune's 

 orbit being 1-22. 



Prof. Russell has calculated the proportion of the 

 thirty-one comets that would pass within 0-5 of each 

 orbit on the hypothesis of chance approach, and finds 

 that it is six for Jupiter, three for Saturn, one and a 

 half for Uranus, and one for Neptune. Hence he 

 concludes that the observed figures give little evidence 

 of capture by any of the planets. 



There is, however, a point not noticed by Prof. 

 Russell, which is that the periods under a century 

 range themselves into four definite groups, the mean 

 period of each group being about 04 of that of one 

 of the giant planets. This gives strong ground for 

 postulating a connection with these planets. Since 

 Halley's comet has been observed for more than two 

 thousand years, there is no difficulty in assigning to 

 it a life dating back to the time when its orbit 

 intersected that of Neptune. The longer the period 

 of a comet the less frequent are the occasions when 

 it is subject to serious disruptive influences, and con- 

 sequently its disintegration is likely to be less rapid. 

 It appears to the writer of this note that Proctor's 

 suggestion that the periodic comets are the products 

 of eruptions from the giant planets deserves more 

 attention than it has generally received. 



