BADIOMETEB. 644 RADISHTCHEFF. CBOOK&8 BADIOMETEB tically all the air has been exhausted; one face of each vane is coated with lampblack, while the other is polished. In the radiometer of Crookes theie are four such vanes carried on a little framework, not unlike a wind- mill Willi four arms; and this being pivoted can revolve around an axis. In the form as used by Nichols ^ there are several moaifica- ' tions, the most important of which is that the mica vane can no longer revolve freely, but can simply turn through a small angle. In a space so exhausted us that around the mica vanes, the particles of the gas are few in number comparatively, and their mean free path may be over a centi- meter. If, now, ether-waves fall upon the polished surface of the mica, they are reflected and have no action, but if they fall upon the blackened surface they are absorbed, and the temperature of this sur- face is raised. As the particles of the gas now impinge on this heated surface they rebound with an increased velocity, and therefore produce an increased re- action" against the surface, pushing it back- ward. If a Crookes radiometer be exposed to a match, or even the hand if sufficiently close, the mica vanes are set revolving at a high speed. If the gas around the vanes was at ordinary pres- sures, the molecules would be so close that any increased velocity of the rebounding particles ■would be transmitted almost instantly through- out the whole gas and so be felt on the polished side as well. Thus there would be no resultant force on the vanes. In the form of instrument used by Nichols it becomes one of the most sensitive thermometers known, and it can measure most accurately the energy of the ether-waves which its vane absorbs. Radio-Micrometer. This is an instrument in- vented by Vernon Boys to measure the energy car- ried by ether-waves. It is a combination of a thermopile and a galvanometer with fixed mag- nets and movable coils. A loop of wire is sus- pended between the opposite jioles of a horseshoe magnet, with its plane parallel to the line join- ing the poles; the two ends of this loop are pro- longed out of the magnetic field and joined liy a wire of a dift'erent conductor. Only the junction of the two different metals is coated with lamp- black (if the waves in question are due to ordi- nary thermal radiations), and exposed to the radiation, the other junction being shielded. The radiation being absorbed by the lampblack pro- duces a rise of temperature; this causes a ther- mo-electric current; and thus the loop of wire is turned through an angle which may be meas- ured by ordinary means. If the instrument is to be used for measuring the radiation of waves produced by electrical oscillations, a sliuhtly dif- ferent plan is adopted at the thermal junction. Consult Preston, Theory of Heat (New York, 1891). EADIOPHONE (from Lat. radius, ray 4- Gk. tpui^ri, /j/i^jr", voice, sound). An apparatus ■for the production of sound by the action of light upon a selenium cell in circuit with a telephone. Alexander Graham Bell and Sumner Taintor in 1880 discovered that if a rapidly intermitting beam of concentrated sunlight was allowed to fall upon a selenium cell (see Selenium), the variations in the resistance of the cell would produce variations in the current which, Howing through a telephone in circuit with the cell and a battery, would cause a sound to be emitted corre- sponding to the original sound which caused vi- brations in the beam of light. BADISH (OF., Fr. radis, from Prov. raditz. It. nidicc. radish, root, from Lat. radix, root). A garden vegetable, RapluDius sativus, of tVe natu- ral order Crucifene, probably a native of Asia, cultivated in temperate regions for its fleshy roots, which are eaten raw. The plant attains a height of about three feet and bears white or lilac-colored blossoms on a branched flower stalk. There are two main types of radishes. The sum- mer varieties are annuals and the winter peren- nials. Both types produce turnip or carrot- shaped white or red roots with intermediate forms. Many winter kinds are black. The flesh of all sorts is white. Under favorable conditions the summer varieties, which are most used for forcing, may produce edible roots in three weeks or even less. They are commonly grown between the rows of slower growing crops like lettuce or beets. In beds the seeds are grown in rows about eight inches apart with one or two seeds to the inch. Radishes grow best on a rich sandy loam soil. They are planted for a succession about every ten days throughout the summer. Winter radishes are" sown in July or in early Au^nist. They are usually larger than summer sorts and have much firmer flesh. They are stored oyer winter like turnips. Another species of radish {Raphanus caiidatus) is cultivated as an escu- lent in Japan, where it is native. The sea-radish (Raphatius maritimus) has roots of great pun- gency. Horseradisli (q.v.) is a near relative. See Plates of Flowers and of Vegetable.s. BADISH INSECTS. The insects which af- fect the radish plant in the United States are for the most part the same species wdiich are found on cabbage and turnips. One important insect enemv of the plant is the cabbage-maggot, or radisii-maggot (Phorhia brassicw) , which infests the roots of many oleraceous plants. The mag- gots puncture the fleshy root of the radish and make channels through it in every direction, safe- ly beyond the reach of any insecticide applica- tion. " The best remedy consist s in proper meth- ods of fertilizing, and a combination of nitrate of so<la, ground rock, and muriate of potash is recommended. This fertilizer should be applied soon after the plants are up and when the leaves are about an inch long, at the rate of 500 pounds to the acre, and liefore or during a rain. If the application be made at this time it seems to reach the maggots just when they are hatching. The adult iiies, which are small ))rovn cieatures, rather smaller than the house-fly. lay their white and slender eggs in little masses on the surface of the ground near tlie infested plants. The mag- gots soon hatch, and the injurious work begins, the species is closely allied to the onion maggot. See Cabbage Insects ; Onion Insects. RADISHTCHEFF, ra-dish'ch&f. Alexander NiKOLAiEViCH (1749-1802). A Russian author and reformer, born in Moscow of an excellent
