Question

pennsylvania to new orleans. they trained their cameras on the transformations wrought by the civil war and by new enterprises including tourism and industrialization, particularly the advent of the railroad. initially celebrating the march of progress, eastern photographers later addressed the destruction of the wilderness and the need for its preservation. balancing nature and culture, the photographs on display present a vision of a nation filled with natural wonders, brimming with innovation, and undergoing rapid yet unstoppable change.
the early decades: 1840s - 1850s
photography was introduced to the world in 1839. when the new medium arrived in the united states that year, it first established itself in major cities in the east. photographers based in philadelphia, new york, and boston recorded the scenic vistas of tourist destinations such as white mountains and niagara falls, first photographed by hugh lee pattison in april 1840. many early practitioners came to the medium from scientific or mechanical backgrounds, drawn to its seemingly magical ability to reproduce nature. and most - including pattison - adopted the daguerreotype, named after its french creator louis - jacques - mandé daguerre. this process fixed an image onto a silver - coated copperplate, characterized by a mirrorlike surface and precise detail, the daguerreotype dominated photography in the united states for the next decade and a half.
looking northwest from westminster street, providence
the 1850s marked a period of transition. processes that used paper or glass negatives to make positive prints began to be adopted more broadly. although they lacked the crystalline precision of daguerreotypes, paper prints made from negatives were reproducible, a characteristic that encouraged the commercialization of photography and the making of american scenes. by the end of the decade, paper prints had supplanted daguerreotypes.
photography and painting: 1850s - 1860s
exchanges between landscape artists and photographers in the mid - nineteenth century moved the new medium toward more aesthetic concerns. a number of photographers - including john hill and charles lowell - worked side by side with artists in the white mountains, with others taking similar approaches in other parts of the country.
how does the author develop the central idea in the text?
by examining the evolution of photography over particular periods
by chronicling how photography influenced various historical events
by comparing and contrasting the styles of leading figures in photography
by showing how photography moved from being a hobby to a serious profession

Explanation:

The text traces the history of photography from its introduction in 1839, through its early practitioners, and its evolution in processes and uses over the 1840s - 1850s. It describes changes in the medium and its impact on society during different periods.

Answer:

by examining the evolution of photography over particular periods