294 



NATURE 



\yuly 28, 188] 



by the action of water at the temperature of the body with for- 

 mation of corrosive sublimate; and this change is accelerated 

 by the presence of citric acid, sodium chloride, or sugar. 



From analyses and examination of the distillation vessels used 

 in zinc furnaces, Herren Schuize and Steiner {Jahrb.fiir Mineral. ) 

 have found that these vessels contain well-formed crystals 

 of zinc-spindl (or zinc aluminate) along with crystals of tridymite. 

 The authors discuss the bearing of their results on the natural for- 

 mation of minerals of the spinell group in limestones ; they point 

 out that the generally accepted hypothesis that such limestones 

 must have been in a fused state for some time, is not necessary, 

 but that the minerals may have been formed by the action of 

 vapour jienetrating the solid hot limestone. The action of gases 

 on a softened rock mass may give rise to molecular changes 

 resulting in the production of various minerals. 



PHYSICAL NOTES 



A CONTINUOUS registering thermometer for recording the 

 temperature of the body has just been described by its inventor, 

 M. Marey. It consists of a brass tube communicating %\ith a 

 Bourdon manometer, containing oil, and closed. Any change of 

 temperature, by altering the internal pressure, makes the curved 

 manometer tube curl more or less, and to it is fixed an index 

 which registers the movements by inscribing them on a recording 

 cylinder. The thermometric bulb may be at some distance from 

 the inscribing apparatus, being connected by a flexible tube of 

 annealed copper. Two such bulbs may be applied to different 

 parts of the body, even to the interior. It is possible therefore 

 to note the relations between the temperatures of the interior and 

 exterior of the body. If we remember rightly, an analogous but 

 more portable instrument was suggested some time ago by Mr. 

 Donald Macalister, but we are not aware whether his instrument 

 is yet before the public. 



Prof. E. Lommel describes in Wied. Ann. a new polarising 

 apparatus in which two plates of platinocyanide of magnesium, 

 cut perpendicularly to the optic axis, are used as polariser and 

 analyser, just as in the tourmaline pincette. Such a section of 

 this crystal transmits a blue light, which, when the angle of in- 

 cidence exceeds 2°, is found to be perfectly polarised in the plane 

 of incidence, and it therefore can be used, if tilted to that 

 extent out of perpendicularity to the axis, as a polariser for a 

 pencil of parallel blue rays. One curious point in respect to the 

 behaviour of a thin film thus prepared is the following : — Let 

 ordinary non-polarised light be looked at through the crystal 

 while the latter is normal to the line of sight. A white central 

 spot, perfectly circular in form, and non-polarised, is observed 

 in the middle of a blue field, which is polarised at every point 

 radially. The only other crystals which can be used for polaris- 

 ing pincettes are the tourmaline and herapathite (iodo-sulphate of 

 quinine) : the point of difference bet« een these and the platino- 

 cyanide of magnesium is that while the two former (which are 

 negative crystals) absorb the ordinary ray, and must therefore 

 be cut parallel to the optic axis, the latter absorbs the extra- 

 ordinary ray, and must therefore be cut at right-angles to the 

 optic axis. 



The galvanic properties of carbon have been closely examined 

 by Dr. Hanichi Muraoka, a Japanese student at Strassburg. 

 He determined the specific resistance and the change of 

 resistance with increase of temperature of all kinds of hard 

 carbon, including Siberian graphite, gas-retort carbon, the 

 artificial carbons used for electric lighting by several well- 

 known firms, and even the graphitic compound used in Faber's 

 lead-pencils. The [specific resistance (at 0° C.) of the last 

 was 9520, while that of the first was I2"2. The artificially- 

 prepared carbons ranged from 36'S6 to SS'^S- 1° ^1 however 

 the resistance decreased with a rise of temperature, the coefficient 

 of decrease being greatest for the Siberian graphite, least for a 

 carbon pencil prepared from coke by Ileilmann of Miihlhausen. 

 This result entirely confirms the recent researches of Siemens 

 and Beetz. The thermo-electric powers of the various samples 

 of carbon were also determined, with respect to that of graphite; 

 their thermo-electromotive force was in every case + to graphite, 

 and varied from 423 microvolts for the Faber pencil carbon to 

 9"26 microvolts for the gas-retort carbon (of Parisian manufacture) 

 used for battery plates. 



Herr p. Volkmann observes that in the determination of 

 the specific gi-avity of heavy liquids, such as quicksilver, by 

 means of the specific gravity bottle or pyknometer, the change 



of volume of the vessel caused by the internal pressure may 

 introduce a source of error, especially as the glass vessel may 

 suffer a sub-permanent strain from which its recovery is not 

 immediate. He gives an example of this error in the case of a 

 pyknometer provided with a capillary tube marked in equal 

 divisions. This pyknometer was filled with mercury Tez/w'/t' stand- 

 ing in nieraoy until the top of the column stood at 68 'i divi- 

 sions. On taking it out of the mercurial bath the column fell 

 to 65'4, and on dipping it it again rose to 68'5. The necessary 

 precautions to avoid this error having been taken, a redetermina- 

 tion was made of the specific gravity of distilled mercury at 

 0° C, the density of water at 0° C. being assumed (at Pierre's 

 value) as o'g99S8l. The new value for the density of mercury 

 comes out as I3"5953 ± "0001, which is a little less than the 

 lowest of the values given by Regnault. 



Prof. S. P. Langley has made the following calculation : — 

 A sunbeam one square centimetere in section is found in the 

 clear sky of the Alleghany Mountains to bring to the earth in 

 one minute enough heat to warm one gramme of water by 1° C. 

 It would therefore, if concentrated upon a film of water i-500th 

 of a millimetre thick, one millimetre wide, and ten milli- 

 metres long, raise it 83^° in one second, provided all the heat 

 could be maintained. And since the specific heat of platinum 

 is only o'0032, a strip of platinum of the same dimensions 

 would, on a similar supposition, be warmed in one second to 

 2603° C. — a temperature sufficient to melt it ! 



The alteration of the zero of thermometers after undergoing 

 sudden changes of temperature is a well-known phenomenon, as 

 is also the gradual rise in the zero in thermometers during the 

 first few months after they have been made. M. Pernet has 

 lately examined the question whether the distance between the 

 " boiling point " and the " freezing point " of a thermometer is 

 constant at all different stages of secular alteration in volume 

 of the bulbs, and finds that this is so, provided the freezing point 

 be determined immediately a/ler the boiling point. On the other 

 hand, if the boiling point be determined and a long interval 

 elapse before the zero is determined, there is considerable error. 

 Suppose a thermometer to be (owing to recent heating or to long 

 rest) in any particular molecular state. In this state its reading 

 will probably be in error : but this amount (so far as due to the 

 above cause) may be ascertained by immediately plunging the 

 thermometer into ice, and observing the error of the zero read- 

 ing. In order that a thermometer should read rightly at any 

 particular tempera'ure it should be exposed for a considerable 

 time to the temperature for which exact measure is desired, or 

 else for a few minutes to a slightly /ligher temperature. 



The transparency of ebonite to heat rays may be shown 

 by the following pretty and simple experiment. A radio- 

 meter is set revolving by the light and heat radiated from 

 an argand gas-flame or the flame of a paraffm lamp. When a 

 thin sheet of ebonite is interposed the rotations continue though 

 with slightly diminished energy. But the thinnest sheet of note- 

 paper interposed suffices to check the revolution of the vanes. 



Prof. Graham Bell has sought to prove whether the 

 diaphragms subjected to intermittent radiation in one of the 

 forms of the radiophone did or did not execute mechanical 

 vibrations. The experiment of Mr. W. H. Preece of attaching 

 a Hughes' microphone to the disk had led to negative results. 

 But Prof. Bell has shown that the central region of the disk (on 

 which the rays fall) is set into mechanical vibration ; and he has 

 proved the point by employing a modification of the mechanical 

 microphone of Wheatstone. A stiff metallic wire is fixed to the 

 centre of a thin metallic disk mounted at the extremity of a 

 flexible hearing tube. When the end of the wire is pressed 

 against any vibrating body its sounds are heard, and the vibra- 

 tions at different points of the disk of a radiophone can be 

 successively explored. The vibrations are found to be almost 

 entirely confined to the illuminated area at the centre of the 

 disk. A Hughes' microphone attached to the edges of the disk 

 would therefore not easily give any indications. With this 

 simple apparatus one very curious effect was obtained. An 

 intermitted beam of rays was focussed upon a brass kilogramme 

 weight, and the surface was explored with the point of the 

 metallic microphone. Over all the illuminated area and for a 

 veiy short distance outside it a feeble but distinct sound was 

 detected, but not over other parts. 



Mr. Edison has devised a new meter for voltaic currents even 

 more ingenious than the "Weber-meter" which he proposed a 

 year ago to fix in houses supplied with electric lamps. In the 



