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32 to permit the filings in the tube to be thoroughly shaken, it will be found that the tube has lost its magnetic properties on account of deranging the positions of the filings. Each filing, or molecule, be- came a magnet in itself, and so long as they all retained the same position with respect to each other when magnetized, they united in forming the magnet, but the shaking caused the filings to assume other positions, and since they are no longer united, as before, the effect is to neutralize each other. When steel rails are laid for a railroad track, a Space Oi a quarter' of an inch . or so is left between the the ends or joints. This allowance is made for the expansion of the rail in hot weather. A steel rail is 30 feet long, so that on a really hot day the linear expansion is all of a quarter of an inch. That portion out of water of a steel hull 500 feet in length must be several inches longer on a hot day than on a cool day, and several inches shorter on an extremely cold day than when the temperature is about normal. The expansion must cause a displacement of the molecules, and this in turn must lessen the mag- netism to some extent.- On a really hot day the rails on a railroad track will be found' bound close together, so close sometimes that it is difficult to see the joint, causing the rail to look like one piece. Ona cold day the, rails at the joints will be found to spread apart from the effects of contraction. -- Red heat is about 300° F.; the boiling point 212° F- On a really hot day the temperature in the sun is hardly ever more than 115 F. Steel being of greater density than iron it will have a greater expanding power. The specific gravity of steel is Po ana Of iroh 753, Or a-cubic foot of steel weighs 488.75 lbs., and iron 470 pies. inere being more 'molecules to steel than iron on account of its greater density, and the space between the mol- ecules being less, the molecules in pushing apart' must have to ex- pand more than where the mole- ecules are not so numerous. For this same reason iron will contract more than steel. In extremely cold weather the ship's magnetism must vary from the effects of contraction of the steel, since the ef- fect is to cause the nearer approach to each other of the molecules of a body with the result of diminishing its bulk and increasing its density. As a further explanation: MINUTENESS OF PARTICLES OF MATTER. All matter is supposed to consist of exceedingly small particles separated from each other by spaces. So small, indeed, are these particles that we can- not conceive of their size. The follow- TAE Marine REVIEW ing statement will give some idea of their minuteness: The perfume of a rose will fill a large room. Millions of particles must be thrown off from the rose to fill the room so completely; yet, if the rose be weighed with the most sensitive scales when it is brought in, and weighed again after the room is filled with perfume, no loss of weight can be discovered. If the rose be car- ried from room to room until its per- fume is distributed through the whole house, we cannot find that the rose has lost any weight. How -- exceedingly small, then, must these particles be, if millions upon millions of them are thrown off from the rose without any perceptible loss of weight. These small particles are called molecules, and every molecule is separated on all sides from those around it by inconceivably small spaces. The smallest particle of matter that can exist independently of other particles is called a molecule. Atoms make molecules; molecules make masses. A molecule is so very small that the smallest particle of matter visible in the best of modern microscopes contaiis millions of molecules. If a drop of water could be magnified until it appeared to be as large as the earth on which we live, each molecule in the drop thus magnified would still look smaller than a base ball. Even in dense solids, mol- ecules are separated by spaces that are large as compared to their own size. The most powerful microscope will not reveal these spaces or pores, but they exist nevertheless, since water has been forced through solids of the greatest density. ~ We may take a lump of salt, which is a mass, and break it into many pieces; each piece will be a mass. We may take one of these pieces and crush it to finest powder; each grain will still be a mass. We may imagine one of these grains of powdered salt to be divided into so many parts that any fur- ther division will change them from salt to something else; these particles of salt so small that further division would change their nature, are molecules. If one of these molecules is divided, it ceases to be salt; we have instead an atom of sodium and an atom of chlorine. The quantity of 'water constituting a mass is not necessarily great. A drop of water may contain a million animal- cules. Each animalcule is amass as truly as the greatest monster of the land or sea. The dewdrop and the ocean, clusters of grapes and clusters of stars, are equally masses of matter. Lona. QUESTIONS FOR MASTERS AND MATES.--NO. 14. 205. The equatorial circumference of the earth is 24,902 statute miles; what -how much water? is the length of a degree of longitude on the equator in statute miles? 206. The polar diameter of the earth is 7,899.5 miles; what is its polar cir- cumference equal to in miles? 207. What will be the weight of 875 cubic inches of water? 208. An immersed body is equal to three quarts of water; what is its vol- ume ? 209. A cubic foot of oak will displace What is the weight of the water? 210. How much of the volume of a cubic foot of cork floating in water is immersed? 211. A hollow iron cylinder 8-in. in ' diameter with a length of 2 ft. and a weight of 15 lbs. will displace how much of its volume when floated in water? What is the volume of the cylinder ? 212. A cubic foot of ice weighs -57.4 Ibs.; How much of its volume will be under water when floating? 213. The pressure of the. water on the bottom of a tank is equal to the weight of water above it. What is the . pressure of the water on the bottom of a cistern whose dimensions are 8 ft. lone, 4 ft. width and 3. ft. deep,. filled with water? 214. What is the displacement of a floating body weighing 1,000 gross tons? 215. What is the weight of a body having.a displacement of 15 tons? 216. A mass of lead having a volume of 25 cu. ft. loses how much weight when immersed in water? 217. What will be the weight of 2.5 cu.- ft: of lead:'if a cubic inch of lead weighs 6.56 ounces? 218. A ship, 200 ft. keel length, 35 ft. beam, 15 ft. depth, draws 4 ft. for'ard and 12 ft. aft, or' a mean draught of 8 ft. If the ship has square sides and corners, instead of round sides and pointed ends, the volume of that part of the ship immersed would be equal to the cubical contents of a rectangular box having a length equal to the length of the vessel on the water line, a width equal to the beam and a depth equal to the draught of the vessel. Say the round of the bottom and the pointed ends amount to one-third of the volume of the rectangular box; what is the dis- placement of the ship in gross tons and what is her entire weight in gross tons? 219. How many cubic feet of cork will a cubic foot of water buoy up? A substance whose density is greater than that of water will sink in water; a substance whose density is less than that of water will float on water. Iron, steel, lead, etc., etc., have a greater dens- ity than water, since an equal bulk of either will weigh many times more than an equal bulk of water. A cubic foot of water weighs 62.42 lbs., while a cubic