Augnsi 19, 1880] 



NATURE 



375 



Hope. A ring-micrometer was used, the aperture of the telescope 

 and the unsatisfactory illuminating arrangements not permitting 

 the use of the parallel-wire micrometer. The stars of comparison 

 have been observed in the early morning with the meridian 

 circle ; also the 7J mag. star used by Mr. Ellery on February 14. 

 Mr. Gill expresses himself as by no means proud of his observa- 

 tions, the comet's nucleus being an object which could not be 

 satisfactorily observed, but he did his best with the available 

 means. He also writes disparagingly of the ring-micrometer, a 

 tool which we incline to agree with him has been very much over- 

 lauded. As Mr. Gill will no doubt communicate tlie details of 

 his observations and reductions to the Royal Astronomical Society 

 or the Astronomische Nachrichicn, we shall confine ourselves to 

 appending his final results : — 



CapeM.T. App. R.A. App. N.P.D. 



1. 10 ... 8 50 2 



— - 8 52 49 

 'II ... S 33 4 



— ... 8 45 42 

 12 ... 8 42 18 



— ... 8 42 iS 

 [13 ... 8 30 57 



14 ... 8 23 5 



— ... 8 42 SI 



— ... 8 42 51 



15 ••■ 8 24 31 



o 3 58-59 



O 20 22'l6 



O 20 31-53 



o 36 28-06 



o 36 28-29 



51 39-32 



1 6 7-89 

 I 6 19-25 

 I 6 19-79 

 I 19 54'92 



123 43 i5'53 



123 31 30-78 

 123 II 33 '93 



— 23-44 

 122 44 20-93 

 122 II 17-23 

 122 10 52-S6 



— S7'i9 

 121 32 5217 



On February 12 two, and on February 14 three, comparison 

 stars were employed. The observations are not yet corrected 

 for parallax. 



PHYSICAL NOTES 



Prof. O. N. Rood claims to have produced a nr,.o improve- 

 ment into the Sprengel pump, by which he says he can easily 

 exhaust to -ginrTinrtnr or i-w^^hyrrwTi- The alleged improvement 

 is in two parts; the first being an arrangement whereby "the 

 mercury, instead of being at once introduced into the pump, 

 passes beforehand through an exhausted bulb " ; the second 

 being a "theoretically perfect fluid valve," formed by bending 

 the fall-tube into a crenellated form at one point. It is hardly 

 necessary to point out that neither of these improvements is new. 

 The first has been adopted in the Sprengel pumps sold by instru- 

 ment makers in London for the last ten years, and the second, in 

 a form superior even to that of Prof. Rood (since the fall-tube 

 was fm-nished with more than one fluid valve of a form identical 

 with that devised by Prof. Rood), was to be seen in one of the 

 improved Sprengel pumps exhibited in the Loan Collection at 

 South Kensington in 1S76. 



M. Trouv£ has suggested a new improvement in the old and 

 simple longitudinal armature employed by Siemens in his earlier 

 magneto-electric machines, and lately revived by M. Marcel 

 Deprez in his little motors. RL Trouve's improvement consists 

 in constructing the armature, not with parallel sides, but witli 

 sides forming part of a skew-cylinder. Thus one part of the 

 armature is ready to leave the poles of the field magnets when 

 the other is approaching it, and the currents produced are there- 

 fore much more nearly continuous than with the parallel form. 

 This will probably be a considerable advantage in the case where 

 the armature is employed in a small motor, which will be driven 

 much more steadily than has liitherto been possible. With three 

 cells of Reynier's new battery this little motor wiU drive a 

 sewing-machine. 



M. J. Plateau proposes a method of estimating approxi- 

 mately the apparent distance at which the moon seems to 

 different people to be in the sky. This means consists in looking 

 at the moon steadily until the retina is sufficiently fatigued to 

 produce an "accidental" image or ghost. The observer must 

 then turn his gaze to a blank wall, on which he will see the 

 accidental image projected as a tinted patch of the same shape 

 as the moon. He is then to retreat from, or advance to, the 

 wall until this image appears to him to be of the same size as the 

 moon itself did. The distance measured off between the observer 

 and the wall will be the same as that at which he unconsciously 

 takes the moon to be. One of the sons of the author having 

 made this experiment, found the distance to be in his case about 

 fifty metres. This seems a small distance, but it was the result 

 of a single experiment under circumstances which were not 

 very favourable. M. Plateau concludes the brief memoir on the 



subject, presented by him to the Belgian Academic, by cautioning 

 all persons who may be interested in the subject to take care in 

 repeating the experiment lest the great brilliance of the luminary 

 should damage their sight. 



M. Reynier recommends as a powerful and constant battery 

 for electric light work a modified Daniells' cell, in which the 

 z^nc is immersed in a solution of caustic soda placed in a rectan- 

 gular porous cell of parchment paper. The electromotive force 

 of this combination varies from i -47 to I -35 volts, and the 

 resistance may be less a Thomson's tray battery. The actual 

 energy which a cell of this battery would furnish is calculated to 

 be twice that of the ordinary round Bunsen cell. 



A FEW months ago Prof. Boltzmann of Vienna published a 

 calculation of the velocity of the electric current in a conductor 

 based upon the discovery of Mr. E. H. Hall that a magnet acts 

 upon a current in a conductor, tending to alter its path in the 

 substance of the conductor. In the July number of the Aiiurican 

 yournal of Science Mr. Hall combats Boltzmann's calculation, 

 and shows that by parallel reasoning a current should tend to 

 urge forward with considerable force the conductor through 

 which it flows ; which mechanical effect is certainly non-existent. 

 Mr. Hall now gives us the very interesting additional piece of 

 information that the displacing force exercised by the magnet 

 upon the current in the conductor is in an opposite direction in 

 gold to what it is in iron— which is also quite irreconcilable with 

 Boltzmann's theory. 



An improved centrifugal machine for schools is described in 

 the Nachrkhtcii of the Gottingen Society of Sciences (No. 9), 

 by Herr W. Holtz. The driving-wheel runs in a vertical plane, 

 and the quick axis may (with one and the same length of cord) 

 be set either in a horizontal or a vertical plane, and higher or 

 lower, also at varied distance from the frame of the machine ; 

 further, it can be so rotated that an object to be rotated with it 

 can be suspended from it. On the same axis and of equal size with 

 the large driving-wheel, but independent of it, nins another 

 grooved wheel. The endless cord passes under these and round 

 two smaller wheels higher up, one of which is on the axis to be 

 quickly rotated (which is set in a movable support). The machine 

 has been patented in Germany. 



In a communication to the Gottingen Society of Sciences 

 {Nachr., No. 13), Herr Wohler states that with aluminium alone 

 and witli very few elements, a g.alvanic battery may be formed 

 of strength sufficient to deflect a magnetic needle strongly, 

 decompose water, and raise a thin platinum wire to glow. ^ In a 

 cylindrical glass vessel holding very dilute muriatic acid or 

 dilute soda lye, is placed a roll of sheet aluminium, and within 

 this a porous cell containing concentrated nitric acid and a 

 smaller roll of aluminium. A projecting piece of the metal from 

 each roll is inserted in a circular cover of_ebonite. 



During a recent thunderstorm at Hamburg the'British Consul, 

 Mr. Pogson, observed the phenomenon of St. Elmo's fire playing 

 above the tip of the spire of a church three-quarters of a mile 

 away. Twenty times within one hour a pale bluish ball of light 

 resembling in tint the flame of burning potassium was seen. It 

 appeared to be spherical in form, and from three to six feet^ in 

 diameter. It seemed to hover above the spire without touching 

 it and lasting about forty seconds at each time of appearance. 



Apropos of the approaching meeting of the British Association 

 at Swansea, w.e may note that on the occasion of the last meeting 

 at Swansea of the Association, in 1S48, a paper was read by 

 Mr F. Wishavv "On the Telekouphon, or Speaking Tele- 

 graph." This antedates Philip Reis's "Telephon" by several 

 years. 



Another improved bichromate battery is announced, this 

 time by the Silvertown Company. In no essential respect does 

 this batteiy differ from the form knowui as " Fuller's battery," 

 save in the addition of certain ' ' exciting powders " to the liqnids, 

 a "grey compound" being dissolved in the inner cell in which 

 the amalgamated zinc is placed, and a "red compound " in the 

 outer cell with the carbon-rod. The use of dUute sulphuric 

 acid is avoided by employing the "grey compound;" the 

 avowed aim of this change is the increase of internal conduc- 

 tivity. The result is certainly an increase of cost. 



Speaking of bichromate batteries, it appears to us that the 

 true function of the porous cell now usually employed with them 

 is entirely misunderstood. The bichromate solution, as reduced 

 by the zinc in the cell on standing, is a colloidal substance. The 



