own weight above. It is recorded that the old hollow trunk at Teneriffe has served more than once for a temple for the performance of religious rites-firstly by the Guanches, and later, in 1493, by the Spanish conquerors.

The name of Dragon tree, or Dragon's-blood tree, appears to be derived from the resin which exudes from the trunk, and is known as dragon's-blood, though the dragon's-blood of commerce is chiefly obtained from Calamus Draco, an East Indian palm. The Guanches appear to have used the resin of the Dracaena for embalming their dead, for it has been found within their sepulchral caves.

In the Museum at Kew are preserved two relics of the old tree, namely portions of the branches, one about ten feet high and one foot in diameter.

ACKLAND'S DIVIDING MACHINE.

MR. ACKLAND (of Messrs. Horne and Thornthwaite's) is well known as one of the few opticians who dignify their occupation by original talent and scientific culture, and he has recently perfected a method and a machine for dividing instruments according to any scale which admits of calculation. The original purpose of Mr. Ackland's invention was to give a practical answer to a demand made by Mr. Glaisher for a mode of dividing alcohol thermometers, so that the inequality of the degrees should exactly correspond with the inequalities in the ratio of that fluid's expansion, when exposed to a gradually rising temperature. The problem may be better understood if we say that degrees of equal magnitude in a tube of uniform bore do not correspond with the spaces occupied by alcohol as it rises in temperature from a low point of the scale to a high one, or vice versa. In a paper read before the Meteorological Society, Mr. Ackland remarks that "it is well known that the expansion of alcohol by heat is not proportionate to its change of temperature; and we are consequently unable to express its corresponding co-efficient by a simple formula, as for metals and mercury, but must adopt the more complex formula of M. Biot.

d = at + bt2,

where a and b are the required co-efficients, and t the temperature." The co-efficient of dilatation for mercury is not the same for all temperatures, but the errors resulting from disregarding this fact amount to very little. Not so with alcohol, for if an alcohol ther

mometer is marked off correctly at a few positions ten degrees apart, and the interspaces are graduated equably, the errors will be found sufficient to vitiate all nice observations. Now it is apparent that any dilatation conforming to a known law of increment, differing from a simple scale, can be represented by degrees, the magnitude of which varies as the law directs; and Mr. Ackland's object was to devise a machine which would reduce the ruling of lines of this description to an exact mechanical operation.

We shall borrow from his paper in the "Proceedings of the Meteorological Society," the following description of the principle involved in his plan :

"To illustrate this new method I have invented, let us suppose we have ascertained the fixed points, P, Q, R, S, of a thermometer corresponding to equal differences of temperature. And let

It is desired to divide the intervening spaces each into ten divisions, so that each division shall occupy its true position.

"To do this, take any right-angled triangle, A B C, and divide the side A C into ten equal parts by straight lines drawn from B.

B

N

L

Then, if a straight line, as A' C', be drawn parallel to A C, it will be divided into ten equal parts; but if it be drawn not parallel to A C, it will be divided into ten unequal parts."

It is evident from inspection of the diagram, that in proportion as a moveable arm, L N, is raised above the base, A C, the spaces marked off upon the group of radiating lines will differ from each other in magnitude, and that by setting this arm to any particular angle a series of interspaces will be obtained, diminishing in any definite proportion that may be required.

Mr. Ackland's machine is so constructed, that by setting it in this way it will rule off upon glass or other material a scale with any regular degree of increment required. If for any particular purpose an irregular scale were wanted, it would prove equally efficient, provided the positions of the required irregularities were known beforehand. It could, for example, rule a regular scale, and intercalate lines, at any points required.

To facilitate the use of this machine, Mr. Ackland has devised an ingenious mechanical computer; so that if it is determined to rule degrees increasing or decreasing in any known ratio, he can save the trouble of computation, and set his engine to do what is required.

It is evident that in addition to a remarkably perfect graduation of thermometers, hydrometers, etc., this machine may be employed for a variety of scientific work; and we have no doubt, as it becomes known, its ingenious inventor will have numerous applications for its use. Some alcohol thermometers graduated in this way have been highly commended by Mr. Glaisher after careful trials.

PROGRESS OF INVENTION.

GALVANIC BATTERY WITH PICRIC ACID.-The nitrous fumes evolved when a Bunsen battery is at work, render its employment in confined situations very objectionable. If, however, a cell be filled with an aqueous solution of picric acid instead of with nitric acid, and if, instead of dilute sulphuric acid, a solution of common salt be used, a powerful action will be obtained. The addition of a few drops of sulphuric acid to the picric acid solution will greatly increase the strength of the current. This battery will be found very useful for telegraph purposes, and in all cases where the evolutions of nitrous fumes may prove objectionable.

Bour

SEPARATION OF STEARIC AND MARGARIC FROM OLEIC ACID. gougnon has made an emulsion with fat and an aqueous solution of ammonia, by which the oleic acid is easily and completely separated, so that nothing remains but a mixture of stearic and margaric acids to be converted into soap.

ORNAMENTAL BOOKBINDING.-Fish-scales are largely used in the manufacture of artificial pearls. A new application of them has lately been made by Mr. A. Parkes, of Birmingham. He proposes to ornament book covers by fixing them firmly to embossed paper, linen, or other suitable material. He first embosses his material with undulations or patterns,

and then coats it with a varnish, consisting of dissolved pyroxylin, or parkesine and fish-scales. The fish-scales sink, for the most part, to the bottom of the hollows of the embossed surface, the solvent evaporates, and they become fixed, and the light playing on them produces a very pleasing effect, it being strongly reflected by the scales where it strikes at a suitable angle. The fabric or paper, after the application of the scales, can be embossed as well as before. Other materials beside parkesine may be used for the varnish, such as shellac, glue, or gelatine. Mr. Parkes also prepares a varnish with pyroxylin and aniline dye, which, when crystallized, has a metallic lustre, and this is applied to the embossed paper; here also the paper can be embossed, after the application of the varnish. In a similar manner varnish containing bronze powder can be applied to paper before or after embossing. The spreading is effected by a roller.

PURIFICATION OF PARAFFINE.-Impure solid paraffine may be purified by first powdering it, then mixing with it common naphtha, and afterwards subjecting it to considerable pressure. By repeating this operation several times the paraffine may be almost entirely freed from the heavy hydro-carbon oils with which it is contaminated in its impure state.

INKSTANDS.-IMPROVEMENTS IN FOUNTAIN INKSTANDS.-To prevent the ink running over the dipping-pan an independent air passage is made in the body of the inkstand, by which a constant level of the liquid is obtained, and this is produced by the action of a column of air, which causes a pressure upon the passage of the liquid, and thus prevents it from overflowing the dipping-cup. The construction is very simple: the tube is attached to the inner wall of the ink-chamber, in which a hole leading outwards is made, so as to admit the air into the tube, and through this hole, the ink can be poured to fill the inkstand. The lower end of the air passage, which is open, descends an inch or thereabouts below the level of the dipping-cup, between it and the reservoir.

MACHINE FOR HATCHING EGGS.-Some years ago an incubator was made which hatched eggs by application of heat from above. This certainly seems to be the most natural way, as the heat from the hen's body strikes from above downwards. A new hatching machine has been invented and patented by T. Horrex, which acts on this principle, although in the application it is different from the method before alluded to. It consists of a flat case of metal, or other material, to hold water or any other fluid which may be thought desirable; this case rests on a frame or box, and under the lower end of the metal case, which is rounded for the purpose, a small lamp or gas-burner is placed. Mr. Horrex prefers to use a small tray of tin partly filled with oil, upon which is floated a wick; under the other or higher end of the flat case, holding the water, is placed a box or tray of a wedge-like form, for reception of the eggs. The box or tray being of this shape admits of the eggs being placed near to or at a distance from the source of heat, by simply pushing the box or tray

forward, or by withdrawing it just as one would do with an ordinary wedge, and so the heat may be regulated at pleasure. Around the top of the box tubing or list can be fastened to prevent the escape of heat. The box is partly filled with sand and such materials as will assimilate it to a hen's nest. The merit of this invention seems to consist in the easy manner of regulating the heat.

GALVANIC BATTERIES.-The object of the following invention is to make batteries more constant, to work for a longer time, to do away with the formation of dangerous fumes and polarization on the elements or in the porous cells. To accomplish this Mr. C. Bowlay makes use of the following arrangement. A porous vessel is divided by means of one or more porous partition plates, or diaphragms, into two or more separate cells, each containing its own electrolyte, or galvanic element (zinc, copper, carbon, etc.), and the exciting salt or mixture, in the dry, or slightly moistened state, and which can attract moisture from a liquid contained in an outer vessel, in which the porous cells are placed. Thus, for example, in case the porous vessel be divided into two cells, one may receive a zinc plate, or other positive element, and the other a negative element, and the cell be filled with a mixture of flowers of sulphur and chloride of sodium, whereas the other cell is to contain the negative element (copper, carbon, etc.), and be filled with a mixture of sulphate of copper, or nitrate of potash; the porous vessel is then placed in the outer vessel, and the space between them is filled with a mixture of crystals of sulphate of copper, which space may, if wished, receive in suitable opposition, a zinc and a copper plate for forming a second galvanic couple, to be used either alone, or in combination with that of the porous vessel, or be entirely left out of action. The outer vessel and the porous cells are then closed with a suitable cement, through which pass the tongues, or electrodes, for establishing metallic connection, also one or two small tubulated funnels, for allowing the proper quantity of water to be poured into the outer vessel for the solution of the sulphate of copper contained in it. The salts, or mixtures, used in the porous cells, should freely attract water, in order always to keep them in the proper moistened state required for the production of the galvanic current. For this purpose, glycerine, treacle, or other waterattracting substances, may be made use of.

LITERARY NOTICES.

A TREATISE ON ASTRONOMY. By Elias Loomis, LL.D., Professor of Natural Philosophy and Astronomy in Yale College. Author of an Introduction to Practical Astronomy, and a Series of Mathematics for Schools and Colleges. (New York: Harper Bros.; London: Trübner and Co.)-This work will be a valuable and welcome addition to our