the centre, the pair, marked P, being shown as already there. Those at the left hand of the shed are to be slid in, in the same way, when necessary, and pass above the others. I, is a latch, or catch, by which the two platforms are held together, or released, at pleasure. B, are movable steps, for conveniently reaching, charging, and discharging, the platforms.

Although two only of such platforms are represented as extending on each side of the shed, the number to be used is limited only by the convenience with which they may be managed; and this is the case also with their demensions. The mode of managing them also, will admit of being varied, whilst the principle upon which they operate will remain unchanged. Thus, for example, the shed may be made to cover the highest platform, and be itself pushed on, so as to gather all the cars, or platforms, under it, in its progress; the platforms may be in a single row, or there may be two or more rows in width, two being shown in the drawing. The platform may be run under the shed by hand, or by means of a winch with a windlass and ropes, or otherwise.

Having thus fully exemplified the general construction and use of my said apparatus, I wish it to be distinctly understood, that I do not intend, by the examples given, to limit myself thereto, but to vary the same in any way I may think proper, whilst the proposed end is attained by analagous means. What I claim as my invention, is the construction of a rail way, in successive steps, and having upon them cars, or platforms, upon which articles to be dried may be exposed to the sun and air, and which may, in a few seconds, be posited upon each other under a shed, to protect them from the weather when necessary, in the manner, or upon the principle, herein set forth. JOHN PHILBRICK.

Progress of Physical Science.

Absorption of light by nitrous acid gas. Sir David Brewster has found that heat so modifies the absorptive power of this gas for the different coloured rays, that while at ordinary temperatures it has an orange colour, by raising the heat it becomes red, and finally black, not a ray of any colour penetrating it. This gas produces in a spectrum formed from artificial light, dark bands analagous to those exhibited by the solar spectrum. By improving the arrangements and methods of observation originally devised by Fraunhofer, of Munich, Brewster has succeeded in detecting two thousand easily recognised portions of the spectrum, separated by thin dark lines, resulting from the absorption of specific rays.

Apparent irregularities in the dark bands of the solar spectrum, were traced to the greater or less proximity of the sun to the horizon, the effect being greatest when the sun sinks below the horizon.

Sir David Brewster infers from a comparison of the lines in the solar spectrum with those produced in the spectrum from artificial light by nitrous acid gas, that the same absorptive elements which exist in the gas also exist in the atmospheres of the sun and of the earth.

Liquid nitrous acid produces none of the fixed lines above alluded to.

Abstract from Lond. and Edin. Philos Mag. May.

Fact in the theory of vision. On the retina and pigment of the eye of the calamary (Sepia Loligo). It will be recollected that an important argument in favor of that theory of vision which assigns the choroid coat and

not the retina as the seat of vision is drawn from the supposed structure of the eye of the cuttle fish. Mr. T. W. Jones has recently made a new dissection and microscopic examination of the eye of the Sepia, in which he finds that the supposed pigment in front of the retina is not really such, but a nervous expansion of a peculiar texture, tinged of a reddish brown colour, a circumstance which has given rise to the error of supposing it merely a pigment. Lond. and Edin. Philos. Mag January.

Fox's dipping needle deflector. This is a compendious instrument for determining the magnetic dip, intensity, and variation, invented by R. W. Fox, Esq. of Falmouth, England. It consists of a dipping needle accurately poised on an axis passing through the centre of gravity, to be deflected from the position of the dip by two bar magnets fitting into tubes attached to the back of the instrument, and the tubes being capable of motion round the axis of the needle so as to produce a greater or less proximity of the magnets to the poles of the needle. The needle having first been brought into the plane of the meridian, the approximate dip is obscured while the bar magnets or deflectors are not in place. The plate to which the deflectors are screwed is then moved to make a convenient angle with this dip and the magnets inserted the north pole of one near the north pole, and the south pole of the other near the south pole, of the dipping needle. The needle is thus deflected to a certain angle which is measured. The deflectors are then moved by moving the plate which carries them until they make the same angle with respect to the first dip, but on the opposite of it, The needle is thus again deflected, but in the opposite direction, and the half sum of the observed angles is the dip. By varying the position of the deflectors several observations may be obtained on different parts of the limb of the instrument, and, with a greater or less leverage, in the force of terrestrial magnetism. The relative intensities are observed by the amount of deflection produced by the magnets at a given angular distance from the line of dip, or by weights placed upon a flexible cord passing over a wheel attached to the axis of the needle, either with or without the use of the deflectors. A telescope attached to the plate or arm, carrying the deflectors, serves to determine the variation by a star, or by the image formed by a lens upon a plane of plaster of Paris, when an observation of the sun on the meridian is preferred. The readings of the vertical circle on which the needle plays are made accurate by a second graduated circle, placed near to the front of the box and of course between the eye and the needle. Verniers are provided for reading the angle of the deflectors and the azimuths. The instrument is provided with the usual means of levelling. When packed, the magnets form a circuit, with a view to a permanent condition in the several needles, or bars. Ann. Rep. Cornwall Polytech. Soc.

On the electrical relations of certain metals and metalliferous minerals.Mr. R. W. Fox finds that the crystalized grey oxide of manganese, holds a much higher place in the electro-negative scale than any other body with which he has compared it, when immersed in various acids, and alkaline solutions. This and some of the other bodies examined by him, rank thus: 1, manganese; 2, rhodium, loadstone, platinum, arsenical pyrites, plumbago, nearly equal; 3, iron pyrites, copper pyrites nearly equal to the second; 4, salina; 5, standard gold; 6, copper-nickel; 7, silver; 8, copper; 9, sheet iron.

Extract from Trans. Royal Soc. Lond. 1835.

On the properties of liquid carbonic acid. According to M. Thilorier, this liquified gas presents the strange and paradoxical fact of a liquid more expansible than the gases themselves: from 32° to 869 Fahr., its volume

116

267

267

increases from 20 to 29, that is to say, that at 86° Fahr., the increase of volume is nearly equal to half the volume at 32° Fahr. Its expansion is four times greater than that of atmospheric air, which from 32° to 86° Fah. only expands 307 whilst the expansion of liquid carbonic acid on the same scale is 1. If the temperature of a tube containing a portion of liquid carbonic acid is raised, this liquid boils, and the empty space above the liquid is saturated with a greater or less quantity of vapour according to the elevation of the temperature. At 86° Fahr., the quantity of liquid at 32° Fahr. sufficient to saturate the empty space, is represented by a portion of liquid equal to one third of the space in which the vaporization has been effected. At 32° Fahr. the portion of liquid of saturation is only of the space saturated.

The pressure of the vapour formed by the liquified gas from 32° to 86° Fahr., amounts from 36 to 73 atmospheres, which is equivalent to an increase of one atmosphere for every centigrade degree. It is important to observe that the weight or density of the vapour increases in a much greater proportion than the pressure, and that the law of Mariotte is no longer applicable within the limits of the liquefaction. If the density of the vapour is taken for the base of the pressure, the pressure at 86° Fahr. will be equal to 130 atmospheres, whilst the manoscope will only indicate 73 atmospheres. If a tube of glass containing a portion of liquid and a portion of gas be heated, two contrary effects will take place:

1st, the liquid will augment by expansion;

2nd, the liquid will diminish by vaporization.

The thermoscopic effects are very different according as the portion of liquid is greater or smaller to the portion of gas; the liquid in the tube will either expand, contract, or remain stationary. These anomalies furnished the means of verifying the numbers which the preceding researches had given on the expansion and vaporization. According to these numbers, the points of equilibrium above which the liquid increases, and below which it diminishes on the addition of heat, result from such a proportion when empty or full, that at zero the liquid occupies of the whole tube. If the liquid at 32° Fahr. occupies one third of the tube it seems as a retrogade thermometer, of which the liquid increases by cold, and diminishes by heat. If the liquid at 32° Fahr. occupies two thirds of the tube it acts as a regular thermometer; that is to say, the liquid increases and diminishes according to the laws of expansion. This thermometer is limited at 86° Fahr. as at this temperature the tube is entirely filled by the liquid.

The specific gravity of this liquefied gas at 32o is 0.83, water being 1. It presents the singular phenomenon of a liquid which from- 68° to + 86° Fahr., runs through the scale of densities from 0.90 to 0.60. It is insoluble in water, with which it does not mix; but is soluble in alcohol, æther, naphtha, oil of turpentine, and sulphuret of carbon, in every proportion; it is decomposed in the cold, with effervescence, by potassium; it does not act sensibly on lead, tin, iron, copper, &c.

When a jet of liquid carbonic aid is directed upon the bulb of an alcohol thermometer, it falls rapidly to 194° Fah.; but the frigorific effects do not correspond with this decrease of temperature, which is accounted for by the almost absolute want of conducting power, and the little capacity for heat, of the gases; therefore the intensity of the cold is enormous, but the sphere of action is limited in some measure to the point of contact. If the gases have little effect in the production of cold, such is not the case with the vapours, of which the conducting power and the capacity for heat are

not the retina as the seat of vision is drawn from the supposed structure of the eye of the cuttle fish. Mr. T. W. Jones has recently made a new dissection and microscopic examination of the eye of the Sepia, in which he finds that the supposed pigment in front of the retina is not really such, but a nervous expansion of a peculiar texture, tinged of a reddish brown colour, a circumstance which has given rise to the error of supposing it merely a pigment. Lond. and Edin. Philos. Mag January.

Fox's dipping needle deflector. This is a compendious instrument for determining the magnetic dip, intensity, and variation, invented by R. W. Fox, Esq. of Falmouth, England. It consists of a dipping needle accurately poised on an axis passing through the centre of gravity, to be deflected from the position of the dip by two bar magnets fitting into tubes attached to the back of the instrument, and the tubes being capable of motion round the axis of the needle so as to produce a greater or less proximity of the mag nets to the poles of the needle. The needle having first been brought into the plane of the meridian, the approximate dip is obscured while the bar magnets or deflectors are not in place. The plate to which the deflectors are screwed is then moved to make a convenient angle with this dip and the magnets inserted the north pole of one near the north pole, and the south pole of the other near the south pole, of the dipping needle. The needle is thus deflected to a certain angle which is measured. The deflectors are then moved by moving the plate which carries them until they make the same angle with respect to the first dip, but on the opposite of it, The needle is thus again deflected, but in the opposite direction, and the half sum of the observed angles is the dip. By varying the position of the deflectors several observations may be obtained on different parts of the limb of the instrument, and, with a greater or less leverage, in the force of terrestrial magnetism. The relative intensities are observed by the amount of deflection produced by the magnets at a given angular distance from the line of dip, or by weights placed upon a flexible cord passing over a wheel attached to the axis of the needle, either with or without the use of the deflectors. A telescope attached to the plate or arm, carrying the deflectors, serves to determine the variation by a star, or by the image formed by a lens upon a plane of plaster of Paris, when an observation of the sun on the meridian is preferred. The readings of the vertical circle on which the needle plays are made accurate by a second graduated circle, placed near to the front of the box and of course between the eye and the needle. Verniers are pro vided for reading the angle of the deflectors and the azimuths. The instrument is provided with the usual means of levelling. When packed, the magnets form a circuit, with a view to a permanent condition in the several needles, or bars. Ann. Rep. Cornwall Polytech. Soc.

On the electrical relations of certain metals and metalliferous minerals.Mr. R. W. Fox finds that the crystalized grey oxide of manganese, holds a much higher place in the electro-negative scale than any other body with which he has compared it, when immersed in various acids, and alkaline solutions. This and some of the other bodies examined by him, rank thus: 1, manganese; 2, rhodium, loadstone, platinum, arsenical pyrites, plumbago, nearly equal; 3, iron pyrites, copper pyrites nearly equal to the second; 4, salina; 5, standard gold; 6, copper-nickel; 7, silver; 8, copper; 9, sheet

iron.

Extract from Trans. Royal Soc. Lond. 1835.

On the properties of liquid carbonic acid. According to M. Thilorier, this liquified gas presents the strange and paradoxical fact of a liquid more expansible than the gases themselves: from 32° to 869 Fahr., its volume

267

increases from 20 to 29, that is to say, that at 86° Fahr., the increase of volume is nearly equal to half the volume at 32° Fabr. Its expansion is four times greater than that of atmospheric air, which from 32° to 86° Fah. only expands 30 whilst the expansion of liquid carbonic acid on the same scale is 1. If the temperature of a tube containing a portion of liquid carbonic acid is raised, this liquid boils, and the empty space above the liquid is saturated with a greater or less quantity of vapour according to the elevation of the temperature. At 86° Fahr., the quantity of liquid at 32° Fabr. sufficient to saturate the empty space, is represented by a portion of liquid equal to one third of the space in which the vaporization has been effected. At 32° Fahr. the portion of liquid of saturation is only of the space saturated.

The pressure of the vapour formed by the liquified gas from 32° to 86° Fahr., amounts from 36 to 73 atmospheres, which is equivalent to an increase of one atmosphere for every centigrade degree. It is important to observe that the weight or density of the vapour increases in a much greater proportion than the pressure, and that the law of Mariotte is no longer applicable within the limits of the liquefaction. If the density of the vapour is taken for the base of the pressure, the pressure at 86° Fahr. will be equal to 130 atmospheres, whilst the manoscope will only indicate 73 atmospheres. If a tube of glass containing a portion of liquid and a portion of gas be heated, two contrary effects will take place:

1st, the liquid will augment by expansion;

2nd, the liquid will diminish by vaporization.

The thermoscopic effects are very different according as the portion of liquid is greater or smaller to the portion of gas; the liquid in the tube will either expand, contract, or remain stationary. These anomalies furnished the means of verifying the numbers which the preceding researches had given on the expansion and vaporization. According to these numbers, the points of equilibrium above which the liquid increases, and below which it diminishes on the addition of heat, result from such a proportion when empty or full, that at zero the liquid occupies of the whole tube. If the liquid at 32° Fahr. occupies one third of the tube it seems as a retrogade thermometer, of which the liquid increases by cold, and diminishes by heat. If the liquid at 32° Fahr. occupies two thirds of the tube it acts as a regular thermometer; that is to say, the liquid increases and diminishes according to the laws of expansion. This thermometer is limited at 86° Fahr. as at this temperature the tube is entirely filled by the liquid.

The specific gravity of this liquefied gas at 32° is 0.83, water being 1. It presents the singular phenomenon of a liquid which from 68° to + 86° Fahr., runs through the scale of densities from 0.90 to 0.60. It is insoluble in water, with which it does not mix; but is soluble in alcohol, æther, naphtha, oil of turpentine, and sulphuret of carbon, in every proportion; it is decomposed in the cold, with effervescence, by potassium; it does not act sensibly on lead, tin, iron, copper, &c.

When a jet of liquid carbonic aid is directed upon the bulb of an alcohol thermometer, it falls rapidly to 194° Fah.; but the frigorific effects do not correspond with this decrease of temperature, which is accounted for by the almost absolute want of conducting power, and the little capacity for heat, of the gases; therefore the intensity of the cold is enormous, but the sphere of action is limited in some measure to the point of contact. If the gases have little effect in the production of cold, such is not the case with the vapours, of which the conducting power and the capacity for heat are