BEAT. T4S front of the condenser of the lantern. A touch of the finger will heat the bulb sufficient to cause the drop to rise in the tube, and it may be made to descend by simply blowing upon the bulb, or by dropping a little water or ether upon it. Many of the pieces of apparatus for illustrating the expansion of metals by heat are so small that they may be readily projected. Thus Gravesand’s Ring, Pyrom¬ eters, etc. The latter may have a small bit of mirror fastened to the end of the index, and the light so arranged that as the index rises, the beam will move upward. A rise in temperature of only a few degrees can be then shown, and the alcohol flame may be dis¬ pensed with ; the warmth of the hand or a little hot water answering the purpose. FORMATION OF CLOUDS. The condensation of liquid in the form of vapor into minute globules and in the production of a shower of rain may be very well illustrated and projected for class purposes in the following manner : — Place about an ounce of Canada balsam in a Flor¬ ence flask and make it boil. At the top of the flask clouds of globules of turpentine will be seen hovering about, altering in shape very much like sky clouds, and the globules are large enough to be visible by the naked eye. If a cold glass rod be gradually introduced into the flask these clouds may be made to descend in showers. Lawson Tait in Nature. Another: Take a flask of one or two litres capacity ; rinse it out with distilled water, and attach to the neck a cork and glass tube of about twenty or thirty centi¬ metres length. Place the glass tube in the mouth and io