38o 



NATURE 



{March 14, 1878 



When the mercury tube of the so-called electrometer is set up, 

 the two surfaces of the mercury in contact with the acid are, I 

 believe, almost always electrically unequal, that in the capillary 

 being less oxidised than the other, and therefore positive to it. 

 "When the circuit is closed, a feeble current passes which, if it 

 were strong enough, would move the mercury forwards. When 

 a telephone is in action in the circuit, its equal and opposite 

 currents combine alternately with the mercury current which 

 strengthens the impulses in one direction and weakens those in 

 the other ; so that, whilst the sum of the telephone and mercury 

 currents may be able to move the mercury in one direction, the 

 difference of these currents is not able to move it in the other. 

 Hence, I believe, arise the motions in question. 



It of course follows that if, by accident, the potentials of the 

 two mercury surfaces were equal, the telephone currents would 

 produce no movement whatever in the mercury. Moreover if 

 by variation of temperature, or by difference of strength of acid 

 at the contact faces, or otherwise, the mercury surface in the 

 capillary is rendered negative to the other surface, the accidental 

 current set up will be in the opposite direction, and the tendency 

 will be for the mercury to recede in the tube, as was observed in 

 the experiment performed before the Physical Society. 



Mr. Page's experiment will, I have no doubt, suggest a means 

 of deducing the potentials of the telephone impulses. 



Robert Sabine 



After reading the experiments of Prof, Forbes on the tele- 

 phone, in Nature, vol. xvii, p. 343, it occurred to me, as 

 probably it has done to others, that this instrument might be 

 employed in comparing the electrical resistances of wires. 

 Accordingly, two weak cells were connected with the ordinary 

 form of Wheatstone's bridge, and the telephone placed in the posi- 

 tion usually occupied by the galvanometer. The current was 

 rendered intermittent by a small electromagnetic apparatus 

 belonging to an electric bell ; the bell itself having been detached, 

 the intermitter was placed in a separate room, and connected by 

 long wires with the battery and bridge. The German silver 

 •wire of the bridge, having a resistance of "2 ohms, was further 

 lengihened at each end by resistance coils of ten ohms, and it 

 was found that with a little practice one could easily compare 

 two resistances of about two ohms within at least i,CKX)th of the 

 true ratio. 



It was found better to attach the sliding piece to the battery 

 rather than the galvanomeier, and it was exceedingly curious to 

 notice the effect of moving the sliding piece so as to gradually 

 diminish the difference of potential at the two terminals of the 

 telephone, the sound diminishing until at last there seemed to be 

 only a slight uneasiness produced in the ear, which ceased when- 

 ever the contact between the sliding piece and the German silver 

 wire was broken. I have no doubt whatever that with a more 

 delicate instrument than the one employed, which was appa- 

 rently not nearly so sensitive as that used by Prof. Forbes, one 

 could compare with considerable accuracy electrical resistances 

 in this manner. Of course the telephone could also be employed 

 instead of the galvanometer, in comparing the electromotive forces 

 of batteries, and it is my intention to make more experiments in 

 this direction. 



By using a tuning-fork made to vibrate by electricity and a 

 Helmholtz's resonator in conjunction with the telephone, the 

 accuracy of testing may no doubt be largely increased. 



Herbert Tomlinson 



1. If the cavities above and below the iron disc of an ordinary 

 telephone are filled with wadding, the instrument will transmit 

 and speak with undiminished clearness. 



2. On placing a finger on the iron disc opposite the magnet, 

 the instrument will transmit and speak distinctly. It only ceases 

 to act when sufficient pressure is applied to bring plate and 

 magnet into contact. 



3. Connecting the centre of the disc by means of a short thread 

 •with an extremely sensitive membrane no sound is given out by 

 the latter when a message is transmitted. 



4. Ten telephones were connected as represented in the follow- 

 ing diagram, on the principle of a battery joined for surface or 

 quantity. 



From transmitter — 



A, B, C, &c., telephones. 



On receiving a message from the transmitter it could distinctly 

 he heard through any of the ten instruments, althoui^h the current 

 had been split up ten times. (I have no doubt that a greater 

 number of telephones might thus be joined with almost equal 

 effect ; from want of instruments I have not been able to find 

 out the limit.) 



The following experiments were made with a double telephone, 

 constructed by a battery of horse-shoe magnets with iron cores 

 at their ends. The wires on the bobbins were wound in opposite 

 directions, as on an ordinary electro-magnet. 



5. On connecting the similar poles of the coils {as + and +) and 

 joining the remaining similar poles (as— and — ) to line wires the 

 instrument both transmitted and spoke with equal distinctness. 



6. On placing the armature on the horse-shoe magnet no loss 

 of power was perceptible in either transmitting or receiving, nor 

 was there any increase of power on augmenting the number of 

 magnets. 



7. If the inner and outer coils of an induction coil are respec- 

 tively connected with a transmitting and receiving instrument, 

 sound can be distinctly transmitted in either direction. 



8. If an ordinary Leyden jar is interposed in the line wire, one 

 end being in contact with the inner, the other with the outer 

 coating, sound can be transmitted, but it is much weakened in 

 strength. 



9. Bringing the iron cores of the double telephone in contact 

 with the disc and pressing with the fingers against the plate on 

 the other side, a weak current from a Daniell cell produced a 

 distinct click in the plate, and on drawing a wire from the cell 

 over a file which formed part of the circuit, a rattling noise was 

 produced in the instrument. 



Experiments No. i, 2, 3, and 9 tend to show the absence of 

 mechanical vibration. For the Experiments Nos. 4 and 5 I fail 

 to find a reasonable explanation. No. 6 shows that strength of 

 the magnet has nothing to do with the force of the sound pro- 

 duced, the latter being simply the result of a difference of two 

 opposing forces. Nos. 7 and 8 require no explanation. 



The above notes are taken from a paper read by me before the 

 Priestley Club on February i6. 



Bradford Grammar School Aurel de Ratti 



In Nature, vol. xvii. p. 164, there was a notice of a tele- 

 phonic alarum in the shape of a tuning-fork, Thi?, however, 

 requires a fixed and special telephone. The following method 

 of attracting attention requires neither. I venture to send it you, 

 as I have seen no notice of any one having tried it ; but I can 

 scarcely believe it to be the case, as the thing would suggest itself 

 to any one studying the instrument. It is to include a magneto- 

 electric machine in the circuit, when turning the handle produces 

 a series of taps in the telephone audible at a considerable dis- 

 tance. I have not tried it for any long distance — merely fifty 

 yards. The magneto-electric machine was placed in the observa- 

 tory, and the telephone, or rather a battery of three telephones, 

 in my study. The noise was heard at the further end of my 

 dining room, the door of which faces that of the study. 



Rugby A. Percy Smith 



Experimenting with a pair of telephones the other daj', I 

 thought I would try if it were possible to utilise underground 

 pipes as conductors. I therefore connected one terminal of each 

 instrument with the gas and the other with the water-pipes, in 

 two houses placed about thirty yards apart, and found that it 

 was possible to carry on conversation by means of the instruments 

 thus connected. The voices were not as distinct a^* if wire had 

 been used, but singing was very plainly heard. I have not had 

 the opportunity of trying a longer distance j perhaps some of 

 your readers.may test the matter further. 



Bury, Lancashire William Stockdale 



H 



" Mimicry in Birds " 



Owing to the special meaning of late attached to the word 

 "mimicry" by naturalists, the above heading seems liable to 

 mislead when appHed to the fact mentioned by Mr. J. Stuart 

 Thomson (page 361). In answer to his inquiry perhaps you will 

 allow me to quote the following from the fourth edition of 

 Yarrell's "British Birds" (vol. ii, p, 229) with respect to the 

 starling. 



" Its song is as imitative as that of the vaunted Mocking-bird, 



