392 



NATURE 



[August 25, 1892 



less definite than during the last opposition. The spot was 

 estimated to be precisely central at I4h. 4600., and this is I4'3 

 minutes in advance of the time given in Mr. Marth's ephemeris 

 {Monthly Notices, May, 1892). The motion of the spot has 

 therefore shown a considerable acceleration during recent 

 months. Between August 2, 1891, and February 2, 1892, the 

 mean rotation period was ph. 55m. 42'23, but between February 

 2 and August 19, 1892, it was only gh. 55m. 39*33. This is a 

 difference of 3 seconds, and it clearly proves that the motion of 

 the spot is affected by some remarkable variations. A very de- 

 cided retardation set in at the end of August, 1891, and con- 

 tinued to operate until February, 1892, but since that time the 

 spot has exhibited an expected celerity of movement. 



A large number of interesting details are now visible on the 

 planet, but the bright equatorial spots which were so con- 

 spicuous about twelve years ago have virtually disappeared. 

 During my observation on August 19 I saw the third satellite 

 projected on the southern limb of the planet as a bright spot. 



Bristol, August 20. W. F. Denning. 



Numbering the Hours of the Day. 



With reference to Dr. Mill's recent interesting article on 

 " Time Standards of Europe," I beg leave to emphatically 

 take exception to the remark on p. 176, that "the system of 

 numbering the hours of the day from o to 24 has failed to hold 

 the popular fancy," as I maintain that the public has had no 

 opportunity of testing the convenience of such a reckoning. 

 The ordinary standard used in this country being railway time, 

 so long as Bradshaw is printed on the old system of numbering 

 the hours only up to 12, it is out of the question to expect the 

 public to adopt any other. Any number of clock-faces num- 

 bered otherwise, either at Greenwich or all over the country, 

 would not lead people to adopt the new system ; the railway 

 tables must first be altered, and as Braishaw is compiled from the 

 tables of separate companies, probably it would be necessary to 

 approach the numerous railway companies with a view to their 

 considering the subject and deciding upon a common plan. 

 They would have to discuss not only the question of printing 

 the time-tables on the new plan, but also whether it would b^ 

 necessary, as well, to alter all the clock-faces at every station. I 

 am given to understand that one railway company (in the Isle 

 of Wight) for some time printed its tables — if it does not still — 

 with the afternoon hours numbered from 12. to 23 ; though its 

 example, because, I presume, it was of a small and uninfluential 

 line, was not copied by any other company. 



A further difficulty in the way of the public making any 

 change is that the highest authoritative book on time matters — 

 \.\\Q Nautical Almanac, CQm.^T\tA and published by the British 

 Government — still reckons the hours from noon. As a civil day 

 commencing at noon is not suggested, would not the railway 

 authorities have a ready objection to urge, and decline to alter 

 their time-tables while time bearing the name of the national 

 observatory, and used in the national ephemeris, were reckoned 

 on a different plan from that which it is suggested they should 

 adopt ? 



As regards the existing mode of reckoning time, the art 

 of the printer is sometimes called in to show at once, with- 

 out having to refer to the tops of columns or the sides of pages, 

 which half of the day is meant ; thus in the Midland Railway's, 

 and part of the North-Eastern Railway's time-tables thick and 

 thin type show this, and in some other tables a short vertical 

 line appears between the figures of the hours and those of the 

 minutes. 



If the lists of places (p. 176) at which the time of the national 

 standard is kept and not kept are intended to be complete, may 

 I ask if Jersey has yet adopted Greenwich time ? It had not up 

 to 1887, although Guernsey had done so. 



Sunderland, August i. T. W. Backhouse. 



Propagation of Magnetic Impulses along a Bar of 

 Iron. 



If at one end of an iron bar an alternating current ba passed 

 through a coil, will there be a wave propagation of magnetism 

 along the bar ? 



Mr. Trouton {Nature, vol. xlv., p. 42) hoped to find an 

 answer to this question by searching after nodes, when two 

 coils are placed one at each end of the bir, and the same alter- 

 nating current is passed through both coils, or when one coil is 



NO. I 191, VOL. 46] 



employed on a closed iron ring. The search was conducted by 

 a secondary coil connected with a telephone. Mr. Trouton 

 found some places of minimum, but ascertained that these were 

 not the nodes sought for. 



Mr. Trowbridge {Phil. Mag. [5] 33, p. 374, 1892) made use 

 of his phasemeter ; two secondary coils, each connected with a 

 telephone, could slide along the ring on which two large pri- 

 mary coils were placed. Two mirrors on the diaphragms of 

 the telephones permitted to study change of phase by Lissajous's 

 figures. 



From his experiments, Mr. Trowbridge infers that there was 

 no wave-motion along the iron ring ; he believes that the pro- 

 pagation of magnetic disturbances produced by forced oscilla- 

 tions on iron bars is closely analogous to the propagation of heat 

 over these bars. 



Though I agree with Mr. Trowbridge in his conclusions, it 

 seems to me that neither the experiments of Mr. Trouton nor 

 those of Mr. Trowbridge could give any but embroiled 

 results. 



In collaboration with Mr. N. G. van Huffel, Phil. Nat. 

 Cand. at this University, I have made some preliminary ex- 

 periments on this question. Firstly, it became obvious that 

 care must be taken against direct induction of the primary coils 

 on the secondary. Only when the secondary coil which was 

 connected with the telephone was embedded in a mass of copper 

 everywhere 2 '5 cm. deep, with a narrowly closing aperture for 

 the iron bar, these direct effects were eliminated if the distance 

 of the secondary from the primary coil were not too small. I 

 have found no indication that similar precautions were taken in 

 the quoted experiments. 



But secondly, the telephone proved to be not the proper in- 

 strument for conducting the research. In most cases the varia- 

 tion of the magnetic intensity goes too slow to be perceptible by 

 the telephone. 



At one end of an iron bar (5 meters long, i '5 cm. diameter), a 

 primary coil A was placed ; along the bar the secondary coil B 

 (within a mass of copper, and connected with a telephone) could 

 slide. A magnetic impulse was given by sending a current 

 through A. If B were near A, a single tick was heard in the 

 telephone : if the distance between B and A were greater, 

 nothing was perceived in the telephone. However, if the 

 circuit composed of B and the telephone were interrupted by a 

 tuning-fork P, a sound was heard during somewhat one second 

 and a half of the same pitch as the tone of the tuning-fork P, 

 every time the primary current was sent through A, or broken. 

 The intensity of this sound diminished as the distance of B from 

 A increased, but was still perceptible wherever B was placed on 

 the bar. 



Thereupon the primary circuit to which belongs the primary 

 coil A was interrupted by a tuning-fork Q. If no tuning-fork 

 were in the circuit of B and the telephone, then only when B 

 was near A a sound was heard of the pitch of Q ; at a greater 

 distance nothing was heard in the telephone. But if now a 

 tuning-fork P interrupted the circuit of B and the telephone, a 

 continuous sound was heard, even at much greater distances 

 of B from A. When the pitch of P differed slightly from that 

 of Q, beats were perceived, also when the frequency of P was 

 nearly half that of Q. The interpretation of these facts is so 

 apparent, that I need not dwell upon it. But these facts illus- 

 trate the principle on which Van Rysselberghe based his method 

 of simultaneously sending telegraphic and telephonic signals 

 along the same line. 



I believe that the propagation of magnetic impulses along a 

 bar of iron has to be studied in an entirely different way. We 

 intend to make an attempt in this direction ere long. 



Utrecht, July, 1892. V. A. Julius. 



"The Limits of Animal Intelligence." 



Closely in connection with an observation I made the other 

 day with respect to an argument of Prof. Pearson' .s, I should 

 like to say a few words about a paper read by Prof. Lloyd 

 Morgan before the International Congress of Experimental 

 Psychology, on "The limits of animal intelligence." The first 

 proposition he advanced, " That human psychology is the only 

 key to animal psychology," and the deductions he subsequently 

 drew, all implied that our knowledge of human psychology 

 differed not only in degree, but in kind, from our knowledge of 

 that of animals. Of course it is true that my knowledge of my 

 own psychology does differ in kind from my knowledge of that 



