By the 1920s, each state in the United States had passed public laws that stipulated a certain day to be Arbor Day or Arbor and Bird Day observance.

By the late 1920s Potter and her Hill Top farm manager Tom Storey had made a name for their prize-winning Herdwick flock.

By the 1920s, composers of Tin Pan Alley and Broadway used ballad to signify a slow, sentimental tune or love song, often written in a fairly standardized form ( see below ).

By the late 1920s, New York writers other than Fitz Gerald were starting to use " Big Apple " and were using it outside of a horse-racing context.

By the 1920s, the emerging middle and working classes were powerful enough to elect a reformist president, Arturo Alessandri Palma.

By the 1920s, many newspapers had a comics page on which many strips were collected together.

Additional milieu were provided by Chaosium with the release of Dreamlands, a boxed supplement containing additional rules needed for playing within the Lovecraft Dreamlands, a large map and a scenario booklet, and Cthulhu By Gaslight, another boxed set which moved the action from the 1920s to the 1890s.

By the early 1920s, unit operations became an important aspect of chemical engineering at MIT and other US universities, as well as at Imperial College London.

By the late 1920s, Al Capone and the Mob were inspiring not only fear, but piquing mainstream curiosity about the American underworld.

By the 1920s, the U. S. reached what is still its era of greatest-ever output, producing an average of 800 feature films annually, or 82 % of the global total ( Eyman, 1997 ).

By the 1920s Lewis Fry Richardson's interest in weather prediction led him to propose human computers and numerical analysis to model the weather ; to this day, the most powerful computers on Earth are needed to adequately model its weather using the Navier – Stokes equations.

By the 1920s, the idea of an Israelite conquest of Canaan-the story of the book of Joshua-was not supported by the archaeological record.

By the 1920s, Hearst, was the owner of a chain of newspapers from coast to coast.

By the 1920s, the diatonic harmonica had largely reached its modern form.

By the 1920s however the Senate had lost much of its original influence, and hence no sitting senator had been known to have serious aspirations of becoming prime minister whilst remaining in the Senate.

By the 1920s the number of cars had soared to 60, 000.

By the early 1920s, however, the inherent limitations of this type of engine had rendered it obsolete, with the power output increasingly going into overcoming the air-resistance of the spinning engine itself.

By the 1920s psychoanalysts assumed that homosexuality was pathological and that attempts to treat it were appropriate, although psychoanalytic opinion about changing homosexuality was largely pessimistic.

By the late 1920s the resistance movement against colonial rule had gathered widespread support during the mistreatment of the Samoan people by the New Zealand administration.

By the late 1920s, however, those employing only optical and electronic technologies were being explored.

By the late 1920s, economic performance had stabilised, but the overall situation was disappointing, for Britain had clearly fallen behind the United States and other countries as an industrial power.

By the 1920s, however, this boisterous folksiness had diminished.

By the end of the 1920s Corbusier was already an internationally known architect.

By the 1920s, the British Government were seeking a replacement for their book code systems, which had been shown to be insecure, and which proved to be slow and awkward to use in practice.

" By the 1920s, Birmingham was the 19th largest city in the U. S and held more than 30 % of the population of the state.

By 1945, IG Farben had become a majority shareholder in Norsk Hydro.

By far the most common version of the OS was SINTRAN III, developed solely by Norsk Data and launched in 1974.

By the late 19th century, improved instruments were designed which could be mounted in any position and allowed accurate measurements in electric power systems.

By channeling a large electric current through the compressed carbon granules in the microphone, a small sound signal could produce a much larger electric signal.

By definition, it is the amount of energy gained by the charge of a single electron moved across an electric potential difference of one volt.

By convention, electric engine refers to a railroad electric locomotive, rather than an electric motor.

By 1936, the Slingerland company introduced a wooden solid body electric model.

By placing the molecules in wells in the gel and applying an electric field, the molecules will move through the matrix at different rates, determined largely by their mass when the charge to mass ratio ( Z ) of all species is uniform, toward the ( negatively charged ) cathode if positively charged or toward the ( positively charged ) anode if negatively charged.

By the 20th century, earlier mechanical calculators, cash registers, accounting machines, and so on were redesigned to use electric motors, with gear position as the representation for the state of a variable.

By the 1970s, because of the advent of psychedelic art, artists became used to brighter pigments, and pigments called " bright indigo " or " brite blue-violet " that are the pigment equivalent of the electric indigo reproduced in the section above became available in artists ' pigments and colored pencils.

By 2007, electric bicycles were thought to make up 10 to 20 percent of all two-wheeled vehicles on the streets of many major cities.

By the time Edison introduced his new alkaline battery, the gasoline powered car had so improved that electric vehicles were becoming increasingly less common, being used mainly as delivery vehicles in cities.

By 1889 the first 6 electric charter boats were working on the Thames and in the 1893 Chicago World Fair 55 carried more than a million passengers.

By purchasing green electricity it is possible to operate electric boats using sustainable or renewable energy.

By the 1970s, because of the advent of psychedelic art, artists became used to brighter pigments, and pigments called " Violet " that are the pigment equivalent of the electric violet reproduced in the section above became available in artists pigments and colored pencils.

By using common generating plants for every type of load, important economies of scale were achieved, lower overall capital investment was required, load factor on each plant was increased allowing for higher efficiency, a lower cost for the consumer and increased overall use of electric power.

By applying a bias voltage to a " gate " terminal, the channel is " pinched ", so that the electric current is impeded or switched off completely.

By the early 20th century, Richmond had an extensive network of electric streetcars, as show here crossing the Mayo Bridge across the James River, ca.

By 1905 the island had electric power supplied by water power in Sun-Moon Lake, and in subsequent years Taiwan was considered the second-most developed region of East Asia ( after Japan ).

By 1990, Sinclair Research consisted of Sinclair and two other employees, and its activities have since concentrated on personal transport, the Zike electric bicycle, Zeta bicycle motor and the A-bike folding bicycle.

By the late 1990s, NiMH batteries were being used successfully in many fully electric vehicles, such as the General Motors EV1 and Dodge Caravan EPIC minivan.

By way of contrast, Gauss's law for electric fields, another of Maxwell's equations, is

By separating positive and negative charges, electric potential difference is produced, generating an electric field.