12) achene. The Columbia Encyclopedia, Sixth Edition. 2001
...Achenes are indehiscent, i.e., they do not split open at maturity. The so-called seed of a sunflower is an achene; the shell is the wall of the fruit, and the true...

13) hat. The Columbia Encyclopedia, Sixth Edition. 2001
...The first hat, which was distinguished as such by having a brim, was the felt petasus of the Greeks, which tied under the chin and was worn by travelers. The decorative...

14) microscope. The Columbia Encyclopedia, Sixth Edition. 2001
...Simple MicroscopesA magnifying glass, an ordinary double convex lens having a short focal length, is a simple microscope. The reading lens and hand lens are instruments...

15) capacitor. The Columbia Encyclopedia, Sixth Edition. 2001
...Simple capacitors consist of two plates made of an electrically conducting material (e.g., a metal) and separated by a nonconducting material or dielectric (e.g.,...

16) limpet. The Columbia Encyclopedia, Sixth Edition. 2001
...Atlantic and the Pacific oceans. Certain species creep over rocks, feeding on algae during high tides, but when the tide recedes they return instinctively to the...

17) perturbation. The Columbia Encyclopedia, Sixth Edition. 2001
...The term is also used for the effect produced by the perturbation, e.g., a change in the object's energy or path of motion. One important effect of perturbations...

18) wheel and axle. The Columbia Encyclopedia, Sixth Edition. 2001
...The effort (applied to the wheel) needed to overcome the resistance (acting upon the axle) is relatively small. The mechanical advantage gained by the use of the...

19) cam, mechanical device. The Columbia Encyclopedia, Sixth Edition. 2001
...There are cams of many diverse shapes, e.g., oval, elliptical, and scalloped-edged, each shape being designed to induce the particular kind of motion required in...

20) electric circuit. The Columbia Encyclopedia, Sixth Edition. 2001
...When the connections are made properly, current flows, the circuit is said to be "closed," and the lamp will light. The current flows from the cell along one wire...