KEY AND INDEX 



Direct Current. A current of electricity generated by a 

 dynamo provided with a system of commutators through which 

 the electric impulses are made to flow in one direction, instead 

 of oscillating as they do in the so-called alternating current. 

 For fuller information see the subject "Electricity," and its 

 various departments. 



Dissipation of Energy. See Energy. 



Dissociation. A hypothetical chemical process (so named by 

 Ste. Claire Deville), according to which the chemical atoms in 

 any compound are constantly separating and reuniting. See 

 "Chemical Affinity," Vol. IV, p. 57. 



Ductless Glands. Certain glands in the animal body that have 

 no excretory ducts, their functions being performed through the 

 channels of the vascular and lymphatic vessels. The spleen, the 

 thyroid gland, and the supra-renal capsules are important ex- 

 amples of this type of gland. See "Blood Corpuscles, Muscles, 

 and Glands," Vol. IV, p. 135. 



Dye. The generic name given to coloring matters in trans- 

 parent mediums; suitable therefore for coloring fabrics or stain- 

 ing surfaces without providing a protective covering such as is 

 given by paints proper. The distinction between dyes and paints 

 is, however, not always very clearly adhered to. See "Paints, 

 Dyes, and Varnishes," Vol. VIII, p. 314. 



Dynamics. The science that deals with the motions of bodies, 

 and with the forces that actuate these motions; in contradistinc- 

 tion to "statics," which deals with stationary bodies. 



Dynamo. The apparatus, consisting essentially of a coil of 

 wire conveying a current of electricity and made to revolve in 

 a magnetic field, which transforms molar energy (usually sup- 

 plied by a steam engine or by a water-wheel) into electrical 

 energy. The multitudinous practical applications of electricity 

 to the supplying and transmitting of power (trolleys, elevators, 

 etc.) are dependent upon the dynamo, the perfecting of which 

 took place late in the nineteenth century. See "Man's Newest 

 Co-laborer: The Dynamo," Vol. VI, p. 171. For Faraday's ex- 

 periments leading up to the development of the dynamo, see 

 "Faraday and Electro-magnetic Induction," Vol. Ill, p. 240. 



Dynamo-electric Machines. Name originally applied to all 

 machines intended to perform work with the aid of electricity, 

 subsequently contracted to "dynamo." 



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