WDS Publishing

Most students of electricity begin their study with what is known as direct current (DC), which is electricity flowing in a constant direction, and/or possessing a voltage with constant polarity. DC is the kind of electricity made by a battery (with definite positive and negative terminals), or the kind of charge generated by rubbing certain types of materials against each other. As useful and as easy to understand as DC is, it is not the only “kind” of electricity in use. Certain sources of ele

This collection consists of African-American sheet music dating from 1850 through 1920. The collection includes many songs from the heyday of antebellum black face minstrelsy in the 1850s and from the abolitionist movement of the same period. Numerous titles are associated with the novel and the play Uncle Tom's Cabin. Civil War period music includes songs about African-American soldiers and the plight of the newly emancipated slave. Post-Civil War music reflects the problems of Reconstruction a

It was discovered centuries ago that certain types of materials would mysteriously attract one another after being rubbed together. For example: after rubbing a piece of silk against a piece of glass, the silk and glass would tend to stick together. Indeed, there was an attractive force that could be demonstrated even when the two materials were separated: