SCIENTIFIC NOTES.

CONTINUING his researches on the repulsive force resulting from radiation transmitted through rarefied gases, Mr. Crookes constructed a torsion balance in which the beam for carrying the experimental disks was a straw suspended by a very fine glass fibre. His experiments extended over one hundred different substances, and he measured the effect produced by them, not only under the influence of simple radiation from a luminous source, but also by removing the invisible heat rays by the interposition of a water screen. In this manner he found that each substance exercises a more or less distinct action on the absorption of rays. Thus most white powders powerfully absorb the invisible heat rays, while they are almost without action on the luminous rays. On the contrary, black powders powerfully absorb the luminous rays, and only slightly absorb the obscure heat rays, whatever their intensity may be. The different metals present great differences in their action. Iron, for instance, chiefly absorbs the invisible heat rays, while gold is principally acted on by the luminous rays. The substances experimented with may be divided into two classes: Ist. Those whose action is increased by the interposition of water screens with regard to the effect produced on the standard disk; 2nd. Those in which the contrary is the case. Amongst the former may be mentioned copper tungstate, saffranin, precipitated selenium, and copper oxalate; these are more affected by light than by invisible heat. Amonst class 2 may be mentioned chromic oxide, persulphocyanogen, zinc oxide, barium sulphate, and calcium carbonate; these are acted upon more by the ultra-red rays than by the luminous rays. Remarkable effects were also obtained by combining the substances in these two categories on the disk of the radiometer. Mr. Crookes has previously shown that when the exhaustion of a radiometer is carried beyond a certain limit its sensibility gradually diminishes until it becomes absolutely null. He has now come to the conclusion -Ist. That there is a gradual increase in the sensitiveness of the radiometer until the pressure has attained 50 millionths of an atmosphere (0·038 millim.); 2nd. That beyond this limit to 30 millionths of an atmosphere (0.013 millim.) it remains stationary; 3rd. Further still, it sinks rapidly until at 1 millionth (0.00076 millim.); 4th. That at o'2 millionth of an atmosphere (0'00015 millim.) the radiometer refuses to turn even when five candles are put near it. He has also examined the effects of molecular pressure produced directly by heat upon a radiometer with the following results:-(1.) When the apparatus is full of air at the normal pressure of 760 m.m., and a platinum ring was rendered incandescent by an electric current, the direction of the rotation of the vanes and disk was positive, that is to say, that which would be produced by a current of air coming from the platinum ring; this effect must be attributed to the ascending current of hot air. (2.) At a pressure of 80 millims. the disk did not turn. The vanes turned slowly in the positive direction. (3.) At 19 millims no movement was produced either by the disk or by the vanes. (4.) At 14 millims. the disk remained stationary, but the vanes began to turn gently in the negative direction,-that is to say, in a way inverse to their first direction. (5.) At 1 millim. the disk turned in a continuous manner in the positive direction, whilst the vanes turned rather fast in a negative direction. (6.) At o'224 millim. the speed of the disk or the vanes was the same, and their rotative movement was the same. Below that pressure the speed of the rotation of the vanes diminished gradually, whilst the speed of the disk increased, and at a pressure of o'107 millim. the disk turned rapidly in the positive direction, whilst the vanes were motionless. (7.) With a more perfect exhaustion still, at o‘098 millim. a sudden change was seen. The

vanes which had been stationary then began to turn in the positive direction at a speed of 100 revolutions per minute, whilst the disks turned as before, positively, but with less speed. (8.) When the exhaustion was carried beyond o'098 millim. the speed of the two disks and of the vanes increased till it exceeded 600 revolutions per minute, and it did not seem to diminish with the highest rarefaction, which was at oooor millim. According to the most recent determinations the number of molecules contained in a cubic centimetre of air at the ordinary pressure is probably something like

1,000,000,000,000,000,000,000 (one thousand trillions);

consequently, at an exhaustion of oooor millim., 100,000,000,000,000 are still left. This number is sufficiently large to justify the hypothesis-That when the molecules are set in vibration by a white-hot platinum wire they are still capable of exercising an enormous mechanical effect.

Mr. J. W. Groves, of the South London Microscopical Club, after cleaning glass slides for mounting microscopical objects, by one of the usual processes, fastens them together by their edges, after the manner of the well-known artists' sketching-blocks. This is easily done with a pile of slips, by fixing round their edges a piece of ready-gummed tissue-paper, 10 inches long, and of a width suitable to the number of slides, so that, although they are firmly bound together, their surfaces are left uncovered. The block is left to dry, when each slip may be detached by running the thumb-nail round its edges. The surface next the adjoining slip should be used for the preparation to be mounted on, as it is, of course, quite clean, although the exposed one may have become dirty: the fragments of tissue-paper are removed after the mount is completed.

Mr. H. C. Sorby, F.R.S., has described to the Royal Microscopical Society a new arrangement for distinguishing the direction of the axes of doublyrefracting substances. The usual method is to employ plates of selenite of various thickness: this, however, involves great difficulty in selecting one of nearly the same tint as that of the crystal examined under the polarising microscope; and unless this can be done it is impossible to obtain so decided a result that the direction of the positive and negative axes can be seen at once and no consideration be required. Mr. Sorby employs a wedge-shaped plate of quartz, cut parallel to the principal axis, 1 inches long and an inch wide. At its thickest end it is 1-20th of an inch thick, and thins off to the sharpest possible edge: this is fixed on a glass plate so as to leave a space of glass 4-10ths of an inch long by an inch broad beyond this thin end of the quartz. The combined plates are fixed in a brass frame, like that for a micrometer, which slides into the eye-piece. On using polarised light with a crossed analyser over the eye-piece, and arranging the plate so that the part with only glass is in front, we see the object in its normal state, and the rest of the field black, and on pushing forward the quartz wedge we see the field of the microscope crossed with coloured bands, gradually rising from the bluish white of the first order, through all the brighter orders of colours, to the faint reds and greens, and upwards to what cannot be distinguished by the unaided eye from white light. If some crystal, giving any tint, be on the stage of the microscope, we can usually see at once whether the tints are raised or depressed, by the manner in which it alters the colour of the bands; and by pushing the quartz wedge backwards and forwards, there may be no difficulty in finding the exact place where the plate of quartz so exactly neutralises the action of the crystal that it appears black. If this does not occur in any place, and, on the contrary, the tints appear to be raised, the eye-piece and the plate must be rotated through an angle of 90 degrees, and the requisite place can then be easily found. The plate of quartz being so cut that its longer axis is parallel to the principal axis of the crystal, we know that this longer axis is positive, and thus also at once know which is the positive and which the negative axis of the crystal under examination. We can also at once see what is the true order of colour which it gives, since we can readily count it up from the bands due to the quartz alone seen crossing the field of

the microscope. We are also by no means limited to visible tints. The crystal may have such a powerful double refraction, or be so thick as to give apparently white light, and yet, by using the thicker end of the quartz wedge, the tints may be reduced down to those easily distinguished. This simple arrangement secures all the advantages of an unmanageably large number of selenite plates, and all necessary observations can be made with ease and expedition.

A valuable paper on the "Application of the Micro-Spectroscope to the Study of Evergreens was read before the Royal Microscopical Society (November 7th, 1877), by Thomas Palmer, B.Sc. As it would be impossible to give an abstract that would be of any use to the student, and, moreover, the reproduction of Mr. Palmer's spectrum charts would be required, reference is made to the original paper.

Owing to the death of Dr. Henry Lawson, F.R.M.S., and Assistant-Physician and Lecturer on Physiology at St. Mary's Hospital, and formerly editor of the "Monthly Microscopical Journal," that publication will be discontinued. The "Transactions of the Royal Microscopical Society" will for the future be issued by themselves, after the manner of the larger societies.

A mode of examining water microscopically has been contrived by W. L. Scott, Public Analyst to the County of Glamorgan and Borough of Hanley. The chief point in the process consists in the manner of filtering the water, by which the organisms contained in a large quantity of material are retained on a very small portion of the filter-paper. The centre of the filter is rendered impervious by means of a fatty composition, and the texture of the paper rendered more obstructive to the passage of minute organisms by being dipped in a very thin structureless collodion. The process is described in detail in the "Monthly Microscopical Journal" (vol. xviii., p. 239).

In the obituary notices of the Royal Microscopical Society we remark the death of Mr. J. L. Denman. Although not distinguished for any published work in the department of minute structure, he has done that which will endear his memory to every analyst. An honest tradesman, disgusted with the adulteration practised-and unfortunately approved of by the public-in the article in which he dealt, he devoted much time and expended considerable capital in obtaining pure wine. Failing to obtain it from the usual sources, he sought it in other countries, and, in spite of popular prejudice, imported the unadulterated wines of Greece and Hungary. Just before his death he had the satisfaction of introducing pure wine from Spain-a country which, like Portugal, had always prepared its exports to the vitiated taste of the British consumer. His definition of wine was simply fermented grapejuice," in old times coupled with bread as a necessary of life.

The Telephone continues to engage the attention of physicists. A very complete and concise description of the construction and action of the instruments of Reiss, Yeates, Gray, Edison, and Bell is contained in the report of a Lecture by Prof. Barrett, of the Royal College of Science, Dublin, and published by Mr. Yeates, of King Street, Covent Garden.

In a paper "On some Physical Points connected with the Telephone," read before the Physical Society, Mr. W. H. Preece has pointed out that this instrument may be employed both as a source of a new kind of current and as the detector of currents which are incapable of influencing the galvanometer. It shows that the form and duration of Faraday's magneto-electric currents are dependent on the rate and duration of motion of the lines of force producing them, and that the currents produced by the alteration of a magnetic field vary in strength with the rate of alteration of that field; and further, that the infinitely small and possibly only molecular movement of the iron plate is sufficient to occasion the requisite motion of the lines of force. He also pointed out that the telephone explodes the notion that iron takes time to be magnetised and de-magnetised. The instrument forms an excellent detector in a Wheatstone bridge for testing short lengths of wire, and condensers can be adjusted by its means with great accuracy. M. Niaudet has shown, by employing a doubly wound coil, that it can be used to detect cur

rents from doubtful sources of electricity, and it is excellent as a means of testing leaky insulators. Among the facts already proved by the telephone may be mentioned the existence of currents due to induction in wires contiguous to wires carrying currents, even when these are near each other for only a short distance. Mr. Preece finds that if the telephone wire be enclosed in a conducting sheath which is in connection with the earth, all effects of electric induction are avoided; and, further, if the sheath be of iron, magnetic induction also is avoided, and the telephone acts perfectly. It appears that conversation can be carried on through 100 miles of submarine cable, or 200 miles of a single wire, without difficulty, with the instrument as now constructed; but the leakage occurring on pole-lines is fatal to its use in wet weather for distances beyond 5 miles.

M. Demoget, of Nantes, has experimented with two Bell telephones in an open field. He held one of these to his ear, while his son at a distance kept repeating the same syllable with the same intensity of voice into the second instrument. He compared in this way the sound heard from the telephone with that heard from the speaker, and calculated their relative intensities from the relative distances of their sources. From the results M. Demoget concludes that the telephone as a machine leaves much to be desired, since it can only transmit 1-1800th of the original work.

Dr. R. M. Ferguson has contributed some valuable "Notes on the Telephone" to the Royal Scottish Society of Arts. He takes exception to the vibration theory of Bell, viz., that it is the vibrations of the disk to and from the pole of the magnet, in excursions proportionate to the intensity, pitch, and quality of the vocal sounds, that electrically affect the instrument. He submits that at the receiving station it can be proved well nigh to demonstration that it is a molecular tremor or vibration, and not a vibration mechanically produced, that emits the sound; and that this molecular vibration becomes louder the easier the sounding body vibrates. Seeing that there is the most perfect correspondence between the sending and receiving instruments, there is, he says, every reason to believe that the sending instrument exhibits the converse action to the receiving instrument. and that there again sound acts on iron so as to produce molecular changes, the electric power of which is much enhanced by the vibration of the sounding body.

The Molecular Theory of the Telephone has also been the subject of a paper at the King's College Engineering Society, by Mr. C. W. Cunnington, who considers that the vibration of the iron disk of the sending instrument under the influence of sound is amply sufficient to induce currents of electricity strong enough to cause the plate of the receiving instrument to vibrate, and thus to reproduce sound: he also referred some of the sound produced in the receiving instrument to the effect of the undulatory currents on the magnet itself, thus explaining results obtained without the use of a vibrating disk. In comparing the vibrating disk of the telephone with the membrana tympani of the ear, Mr. Cunnington pointed out the fact that the predominance of the fundamental note of a flat plate would drown a large number of the overtones of the voice, thus causing many of the observed peculiarities of the sound transmitted in ordinary telephones; the membrana tympani being funnel-shaped, whilst peculiarly susceptible to the influence of sound, had no fundamental note of its own, and therefore transmitted all of the sound vibrations impinging upon it (within certain limits) without giving undue preponderance to any particular note.

The Count du Moncel finds that the vibratory plate of the recipient cannot merely be replaced by a very thick and massive armature without affecting the transmission of speech, but these vibratory plates may be formed of nonmagnetic substances. The vibratory plate may even be totally suppressed without hindering the telephonic transmission provided the polar extremity of the magnet is placed close to the ear. Hence the vibrations which reproduce speech in the receiving telephone are principally produced by the metallic nucleus infolded by the coil. The vibratory plate serves merely to react for the production of induced currents, when set in vibration by the voice, and by its reaction upon the polar extremity of the magnetic rod to reinforce the magnetic effects produced by the latter.

At a meeting of the Physical Society, in February last, Mr. F. J. M. Page exhibited the action of the telephone on a capillary electrometer. He first explained the construction of Lippmann's electrometer, as modified by Marey, and threw the meniscus of the mercury in the capillary tube on the screen by the electric light. The delicacy of the instrument was shown by passing a current of 1-1000th of a Daniell, which caused a distinct movement of the mercury. Resistances of 500 ohms and 1-50th ohm gave approximately the same deflection, so that, in practice, the instrument may be considered to be independent of resistance, in addition to which it possesses the great advantage of portability, and its indications are almost instantaneous, To illustrate the use of the electrometer for physiological investigations, a frog's heart was connected by non-polarisable electrodes with the instrument: each beat of the heart caused a considerable movement of the mercury column. A telephone was now connected. On pressing in the iron plate the mercury moved, and on reversing the wires the movement was seen to be in the opposite direction. On singing to the telephone each note produced a movement; but the fundamental note of the plate, as well as its octaves and fifths, had the greatest effect. On speaking, the mercury oscillated continually: some letters of the alphabet had scarcely any effect, and the w was especially curious, producing a double movement. Reversing the wires did not alter the character or direction of these movements. The same effect was observed when the telephone was in the primary and the electrometer in the secondary coil of a Du Bois Reymond's induction coil. In conclusion, Mr. Page showed the contractions produced in a frog's leg. On inserting under the sciatic nerve two platinum wires coupled with the binding-screws of a telephone, and talking to this instrument, violent contractions ensued. In the course of the discussion which followed, Prof. Graham Bell said he had made very many attempts to ascertain the strength of the current produced by the human voice in vain; he considered, however, that the present method will in all probability give some most valuable results.

On Thursday evening, January 10th, M. Raoul Pictet succeeded in liquefying hydrogen gas in the laboratories of the Society for the Construction of Physical Instruments, at Plainpalais. The experiment, which was performed in the presence of several people, succeeded perfectly. The process consists in decomposing formiate of potash by caustic potash, a reaction which, as proved by M. Berthelot, gives hydrogen absolutely pure. The pressure commenced to rise at half-past eight; gradually and without any stoppage it attained, at seven minutes past nine, 650 atmospheres, at which point it remained steady for a few instants. At this moment the tap was opened, and a steel-blue jet escaped from the orifice, producing a hissing sound like a bar of red-hot iron plunged into water. The jet suddenly became intermittent, and there could be observed a hail of solid particles projected violently to the ground, on which their fall produced a crackling noise. The tap was closed, and the pressure, which was then at 370 atmospheres, gradually descended to 320, where it remained for some minutes. It then rose to 325. At this moment the tap, on being opened a second time, only allowed a jet to escape intermittently, rendering it evident that a crystallisation had taken place in the interior of the tube. The proof of this can be established by the escape of hydrogen in the liquid state when the temperature begins to rise on stopping the pumps. Thus has been experimentally demonstrated the liquefaction, and especially the solidification, of this gas, which from its properties has always been considered probably to belong to the class of metals.

M. Cailletet sent a paper on the "Liquefaction of Nitrogen, Hydrogen, and Atmospheric Air" to the Academie des Sciences, which was read at the meeting on the 31st of December, 1877. M. Cailletet showed that pure and dry nitrogen compressed to about 200 atmospheres, at a temperature of +13°, then allowed to expand suddenly, condenses in the most perfect manner: it first produces an appearance like that of a pulverised liquid in small drops of appreciable volume; this liquid then gradually disappears from the sides to the centre of the tube, at last forming a sort of vertical column following the axis of the tube. The duration of these phenomena is about 3 seconds. On