Jati. 9, 1879] 



NATURE 



221 



{b) The green pyrochrome of the boric acid was unaltered (no 

 soda). 



[c) The substance floated in the bead in bluish-white, fat-like, 

 amorphous fragments like alumina or opaque silica as tabasheer, 

 but— 



((/) On continued heating, the fragments gradually disap- 

 peared, leaving bubbles, until in half an hour, with fresh boric 

 acid, there was simply a transparent bead left ; exactly the beha- 

 viour of minute fragments of diamond in boric acid. 



Silica is absolutely, and alumina nearly, insoluble in boric 

 acid before the blowpipe. 



One conclusion, therefore, seems this : that a slow solution of 

 charcoal in the water takes place, and that crystals of carbon 

 are deposited upon the aluminium. 



London, December, 1878 W. A. Ross 



Observations on the Microphone 



With regard to an explanation of the action of the micro- 

 phone I observed a fact which, though it was already known 

 from some anterior experiments with strong galvanic currents, 

 has not been remarked, as far as I know, with this instrument. 

 On connecting the current from six Grove cells with the micro- 

 phone (the telephone not being in the circuit) composed of the 

 tluee carbon rods, the vertical one assumes a vibratory motion 

 between its supports, which causes a very audible sound, especi- 

 ally when placed on a sounding-board. 



I think this experiment may serve as another illustration of 

 the well-known fact, discDvered by Ampere, of the repulsive 

 action between the subsequent parts of a rectilinear current. 

 Most of the experimental proofs bearing on this point leave some 

 ■doubt as to a true demonstration, because a dilatation from the 

 heating effect of the very strong airrents used with metallic 

 bodies may interfere, and are considered, for example, to explain 

 the experiments oi Forbes and Gore.^ But in my case, with a 

 substance which has a very small coefficient of dUatation, I think 

 the >-ibratory motion may be considered as an electrodjmamic 

 -effect. As a supporting demonstration, I suspended with insulated 

 metallic wires near another, three horizontal pieces of carbon 

 •(3 cm. long) in such a way that they could move freely away, 

 -and the two outer ones were connected with a battery of twenty 

 Grove cells; immediately on closing the circuit a repulsion 

 -ensued between them and an oscillating motion set in, whilst 

 bright sparks appeared between the contacts. 



This experiment may throw some light on a recent controversy 

 which ha^ arisen between Mr. Varley and Prof. Hughes.^ The 

 latter insists on a change in contact resulting from alternating 

 varying forms of the molecules or their sphere^ of action, in 

 accordance with the sonorous vibrations. Mr. Varley points out 

 a quite distinct cause. By using a contact-breaker moved with 

 <he hand he discovered, on applying a microscope with a 350 

 times magnifj'ing power when the circuit was closed or opened, 

 a grey cloud issuing between the nearest carbon-points. This 

 seems to prove that little particles of carbon are loosened by an 

 effect of trituration on the contact-surface, the cohesion being 

 lessened by the heating effect of the current. This cloud of 

 microscopic dust serves as a vehicle to the current (when the 

 carbon piece is vibrating), and its resistance of course is easily 

 modified by the impinging sound-vibrations. Now my experi- 

 ment, though with a strong current, supports this fact, and 

 shows that the vertical carbon is actually \abrating under its 

 influence, and may prepare the above-mentioned condition, or 

 at le^t render it very ready to change its contact in accordance 

 with sound-waves acting on it with more or less force. 



Perhaps it will be observed that a microphone acts very well 

 in transmitting sound when even the weak current from a couple 

 of Leclanche cells is used, but then, also, we may admit a 

 propensity (through the influence of this current) of the vertical 

 carbon rod to get into a vibratory condition, which the sonorous 

 vibratioiis wiU easily actuate according to their own period, if 

 really it is not abready vibrating at microscopical distances. 



Prof. Hughes alludes to an experiment which, as he thinks, 

 gives an evident support to his theory. In a sealed glass tube are 

 inclosed five loose pieces of carbon with terminals to admit a 

 current. He remarks that, properly pressed mere mechanical 

 shaking produces no variation of the current except that due to a 

 constantly increasing resistance caused by abrasion of the carbon 

 contacts, whUst under the influence of sonorous \'ibrations a 

 varying current is produced, because the tube in this case is 



» r.J^' ^^^-J'"^'}- '^"- P- 353. Gore. ibid. , t. XV. p. 519. 

 TeUgraphicy<nimal, October i and 15, 1878. 



varying its length, and the molecules undergo proportional change 

 of form. I think this proof may be as well, and with more 

 probability explained by the facts mentioned above. The tube 

 contains four or five loose pieces of carbon, and beside these 

 some air, which, as it is in a closed space, will press from all 

 sides on the carbon parcels when it is put in vibration by sound, 

 and therefore alter in a mechanical way their distance, the more 

 because the surfaces in contact are rough ones. In conclusion 

 I will observe that the audible vibration of the vertical carbon 

 rod in the microphone certainly elucidates the facts discovered by 

 Blyth concerning sound transmitted only with coal cinders 

 forming a receiving and a transmitting apparatus in a galvanic 

 circuit, and on which he insists in a recent communication to this 

 journal (Nature, vol. xix. p. 72). L. Bleekrode 



The Hague, ^December 8, 1878 



Shakespeare's -Colour-Names 



In the name of scientific accuracy and fair criticism I protest 

 against Mr. Murphy's letter in Nature, vol. xix. p. 197. His 

 remarks proceed on the perfectly gratuitous assumption that all 

 eagles have blue eyes. As this is not a fact (the only live ones 

 I have examined had both of them green eyes), I have no hesi- 

 tation in asserting that when Shakespeare wrote "An eagle, 

 madam, hath not so green, so quick, so fine an eye as Paris 

 hath," he did so, after ha\ing seen an eagle or eagles, and that 

 when he said green he "evidently " meant green, and not blue. 



Edinburgh, January 4 A. Craig-Christie 



Your correspondent, Mr. J. J. Miurphy, in his letter. Nature, 

 vol. xix. p. 197, overlooks the fact that blue'xi, quite^as inappropriate 

 as green to describe the eye of an eagle. Shakespeare would 

 never have used either epithet ; the word he made use of was 

 doubtless keen. Green has been substituted by the mistake of 

 some transcriber of the play working by ear, and not by eye. I 

 only wonder the correction h^ not been made long ago by some 

 commentator. Robert Brewin 



Exeter, January 4 



The Meteor Shower of January 2 



After a very hea\'y fall of rain, sleet, and then snow (equalling 

 in the aggregate l "472 inch), on the evening and night of January 

 I, the clouds partly cleared away on the ensuing morning, and 

 during a watch of twenty minutes (6' 14 to 6*34 A.M., Januarys) 

 in a sky fully two-thirds overcast, fourteen meteors were seen, 

 all of them belonging to the special shower in Quadrans. This 

 radiant was evidently very active at the time I saw it, and in a 

 cloudless sky, must have supplied meteors at the rate of more, 

 than one per minute (for one observer). The paths were short 

 and quick without streaks or trains. Radiant point at 230° + 51% 

 but not very exactly found owing to the clouds and haze through 

 which several of the meteors were indistinctly seen. Three or 

 four were as bright as 1st mag. stars. W, F. Denning 



Ashleydown, Bristol, January 2 



OUR ASTRONOMICAL COLUMN 



MissiKG Nebula. — In Mr. Ellery's Report, to which 

 reference was made last week, it is stated that "two 

 nebulse, H 4223 and H 1561, widely separated from each 

 other, and described by Herschel as prominent objects, 

 cannot now be found, although careful search has been 

 made for them." The first of these nebulae is near the 

 cluster Dunlop 413: in the "General Catalogue" it is 

 called " a remarkable object," but being very large and 

 faint, it might, perhaps, be suspected that its invisibihty 

 in the Melbourne reflector is owing to the same cause 

 that has led to the Pleiades-nebula, and other similar 

 diffused objects (as G. C. 132, 4570, 5051) being over- 

 looked in ver)' large telescopes though obvious in much 

 smaller ones. But in the case of H 1561 no such sup- 

 position is admissible. It was observed by Sir John 

 Herschel on five occasions, in sweeps made between 

 December, 1834, and February, 1836; when best seen it 

 was termed pretty bright, from 25" to 35" in diameter, 

 gradually brighter towards the centre, and situate to the 

 south of, though verj- near to, three stars of the eleventh 



