any risk of making the subject the easiest one in the high school curriculum, I am sure many desirable changes could be made. The tendency in high school education to-day is unmistakably toward vocational training, and, as physics is so well adapted for this kind of work, we should make a special effort to bring it into conformity with this newer ideal. By changing the content of physics, could we not bring its wonderful wealth of information (that wealth of information which makes the civilization of to-day so much superior to the civilization of the past) within the reach of more of our high school students and so help them to prepare, in a larger way, for vocational service? If the content were reduced in quantity, as I have suggested, it would naturally improve its quality, for it would result in the selection of only the choicest and most suitable material for the work. The retention or rejection of certain material would depend largely upon the after use to which it could be put by the student. The colleges and universities could easily and should adjust themselves to a preparation without the absolute units, if their elimination was found desirable. The main thing to work for is a content that would be more directly connected with the life interests of the child. Is it not an embarrassing fact that our students of physics complete the subject and yet know scarcely anything about the physics of a stove or furnace, or the ventilation of a house or public building? Very few of them would know anything about the switches, fuses, wires, and fixtures that would be needed if they were going to build a house and wire it for electricity. And I doubt if one in a hundred could figure out the cost of running a sixteen candle-power electric lamp for an hour, if given the cost of electricity per kilowatt-hour. Why should this be so? Certainly this kind of material would not only give valuable information, but helpful training as well; and would it not furnish good material also from which to select the content of a high school course in physics? Why should not our high school students, when studying electricity, for example, have the matter of switches, fuses, insulators, wires, and lamps brought to their attention, and why should not these things be studied both from the text-book and from samples as well? Why should they not, in the class, at least, and if possible in the laboratory also, measure the pressure and the current used to operate a sixteen candle-power electric lamp, determine its wattage, and what it would cost to operate it for an hour? If time permitted, why should they not be allowed to measure

the candle-power of the light and determine the cost of operating the same per candle-power hour? If the candlepower, rate of consumption, and cost of gas were previously determined, while studying light, the relative cost of the two methods of lighting could now be compared and the student given valuable information as well as valuable training at the same time. But why take more of your time to multiply examples? Practically all of the content could be brought to the same practical basis. Would it not be worth while to make the change? And would not physics, when so changed, become a more vital subject in high school education than it is to-day?

AN ARCTIC COAL MINE.

According to Le Nature, the most northerly coal mine in the world is that of the Arctic Coal Company (an American concern) at Advent Bay, on the east coast of Spitzbergen. The coal crops out at the surface of the ground several hundred feet above sea level, and is brought down to the harbor by a funicular railway. The company has about a hundred and fifty men at work, chiefly Norwegians, who remain on the spot all the year, although Advent Bay is blocked by ice and inaccessible to vessels for eight months, viz., from November to June. About six thousand tons were taken out last year, but the maximum output has not yet been reached. The chief market for this coal is Norway, which has no coal mines of its

own.

VARIETIES OF MINERAL WATERS.

Various schemes for the classification of mineral waters have been proposed, but none is altogether satisfactory. The substances a water may contain are many, the exact relations between these substances in solutions so dilute, as most natural waters are not known to the chemist, and the possible gradations of mineralization are infinite. These reasons and the additional reason that all the waters in any one class in any scheme of classification yet proposed would not necessarily have the same physiologic action, and hence the same medicinal value, cause the devising of a scheme of classification that will fit all needs to seem impossible. A further matter that may prove of importance in this regard is the occurrence of that unstable element, radium. Radium emanation has been detected in many spring waters, and the presence of the element may explain the cures wrought by some waters that were regarded as only a little mineralized. The radioactivity of a water rapidly decreases, and it is possible that this fact explains why some medicinal waters have greater efficacy when fresh than when they have been bottled for some time.

AN APPARATUS FOR THE STUDY OF THE GAS LAW.

BY HENRY A. ERIKSON, PH.D.,
University of Minnesota.

The object in designing the apparatus described below was to meet a need in the college laboratory, of a simple and compact instrument that will enable the undergraduate to study with a fair degree of accuracy the relation expressed by the gas law PV=RT.

Description of apparatus.-The gas is enclosed in a glass tube 15 cm. long and 1.5 cm. outside diameter, as shown at A in Fig. I. Inside this glass tube and projecting up through the mercury is a steel rod 25 cm. long. This rod throughout its length has threads of one millimeter pitch, is finely pointed at its upper end, and has a micrometer head of 100 divisions at the lower end. The mercury in contact with the gas in A communicates through a rubber tube with the mercury contained in the parallel glass tube B. The glass tube A is surrounded by a glass jacket filled with water which may be heated by passing an electric current through a coil of five turns of No. 24 IaIa wire wound on the stirrer E. The current may be obtained from the house circuit, using a bank of incandescent lamps L connected in series with the coil of the stirrer. As the lamps in the bank are in parellel the current may be altered by connecting or disconnecting the various lamps. All metal parts coming into contact with mercury are of steel and those that come in contact with the water in the jacket are of brass. All packings are of leather. The apparatus is supported by two parallel vertical rods 1.5 meters in height and having a tripod base.

Readings. The volume of the gas is obtained from the micrometer reading when the point of the rod is even with the mercury surface in A, an adjustment that can be made with great accuracy. The volume V when the micrometer is at zero on the scale and the volume per unit length (k) are given from the calibration to be described below. The pressure in centimeters of mercury height is the barometer reading plus the difference in heights of the mercury surface in A and in B. This difference is obtained from the scale C. The slide D carries a vernier and a mirror upon which is an index line which may be placed, free from parallax, even with the mercury surfaces or, in the case of the tube A, even with

the lower end of the rod R. The temperature is obtained from a thermometer suspended in the water surrounding the tube A.

Calibration. The volume per unit length of tube A is obtained, once for all, in the following manner: Remove the rod R and clamp the tube A in an inverted position. Pour in a small quantity of mercury. Replace the rod R and obtain the micrometer reading when the point of the rod is even with the mercury surface. Remove the rod and add a known weight of mercury, sufficient to nearly fill the tube. Replace the rod and obtain the micrometer reading as before, noting also the temperature of the mercury. From the weight of mercury, the density of the mercury at the recorded temperature and the difference between the micrometer readings, the volume (k) per unit length of tube may be determined. The volume for a given micrometer reading may be determined as follows: Remove the rod, hold the tube in an inverted position and admit a quantity of mercury. Replace the rod, close the side tube by means of a screw provided for this purpose, place the apparatus in an erect position, and then turn the rod until the point is even with the mercury surface. Obtain the micrometer reading and weight of mercury and tube. Remove the rod and fill the tube completely with mercury, noting its temperature. Replace the rod and turn until the micrometer reads the same as before, the excess of mercury being allowed to escape through the side tube, and weigh. From the difference between the two weights and the density of the mercury at the observed temperature, the volume corresponding to the micrometer reading may be determined. From this volume. and the value of (k) the volume V corresponding to the zero of the micrometer scale may be obtained.

Boyle's Law, PV=C.-The temperature of the water in the jacket is kept constant. The volume corresponding to different pressures is determined as given above under "Readings." From these the constant C is computed.

Charle's Law, P-KT.-The micrometer is kept constant. The apparatus is raised or lowered by means of an auxiliary screw S until the mercury is even with the point. The pressure and temperature are then determined. The temperature is then raised by passing a current. When the desired rise. has taken place (say 5°) the current is reduced so as to keep the temperature constant. The pressure and temperature are determined as before. From these the constant K is com

puted.

Boyle's and Charle's Laws combined, PV=RT.—The pres