Historic Structures

Jonathan Parker Snow Wrights Covered Bridge, Claremont New Hampshire

The engineer to whom we owe the construction of half our nation's remaining stock of covered railroad bridges was born at Concord, New Hampshire in 1848. His father, Jonathan Snow, was a blacksmith and machinist. His mother, Lydia Ann Parker, died while he was still an infant, and he was raised by an aunt on a hill farm in Nelson, New Hampshire. After attending the local district school, he spent two years at a private academy in Contoocook. Like many young men of his day, he contemplated a career at sea. Later he decided on civil engineering and enrolled in Thayer School of Civil Engineering, associated with Dartmouth College, receiving his degree in 1875.

Snow later told young men that for the first ten years after graduation they should spend no more than two years in any one place, and he followed this advice himself. For the first few years after school he worked at mining in North Carolina, at surveying in Prince Edward Island, and at various other tasks. He also served as an instructor in civil engineering at Thayer and prepared useful course notes on various aspects of the field, as textbooks were then rare. In 1880 he took a position as a draftsman with the Boston Bridge Works and stayed there several years, but he tired of indoor work. Then in 1884 he began service as Bridge Engineer with J.W. Ellis, C.E. in Woonsocket, Rhode Island. In this capacity he had occasion to do work for the Providence & Worcester Railroad.

Early in his railroad work, Snow became convinced that wooden trusses were still efficient, and that they should be maintained in service as long as possible instead of being replaced with iron trusses. Though described as a man of few words, his views on wooden trusses may have led to his selection as Bridge Engineer with the Boston & Maine Railroad in 1888, for this system had many such structures and served a region rich in timber. Snow not only maintained older wooden trusses, but also he built many new ones almost up to his retirement in 1911. He became Chief Engineer at Boston & Maine in 1909, but he retired when the system became associated with the New Haven Railroad. When he left, Boston & Maine stopped building wooden trusses. Snow continued to work as a private consultant with an office at 18 Tremont Street in Boston until his death in 1933.

At the time of J.P. Snow's service, the Sugar River Railroad was part of the Boston & Maine system. He replaced most of the bridges, sometimes using metal riveted trusses or plate girders, but for Wright's Bridge he built a new wooden lattice truss.

Snow always held his own opinions, and in the great debate over steel truss joints, he favored rivets over pins. He advised young engineers to say little but observe much, in essence to "restrain their knowledge until it was needed," and he said that much of value could be learned from workmen on the job. Though married, he had only one child, who died in infancy. His legacy is his engineering work, well exemplified by Wright's Bridge.

In an 1895 article, Snow described his practice in detail. In that year the Boston & Maine Railroad had 1,561 bridges of all kinds, including both overpasses and track bridges. Of these, 1,085 or nearly 70 percent were wood, either trestles, stringers, pony queenposts and Howe trusses, or through Town lattice trusses like Wright's Bridge. Over half the bridge replacements were still being built of wood. For longer through spans, Howe trusses of southern pine cost almost as much as iron bridges, and the local spruce was unsuited to Howe truss work because of its tendency to warp. Spruce was ideally suited to the Town lattice truss. For various reasons, the loads calculated for wooden trusses were somewhat less than those used for iron or steel. While wooden trusses might have a shorter service life, they could be easily reinforced if necessary, and they gave ample evidence of distress long before failure. In 1895, a single-track bridge of 120' span cost about $5,300 in iron, $5,000 for a Howe truss of southern pine with iron angle blocks, but only $3,500 for a spruce lattice. In shorter spans the cost advantage for wood was even greater, but in longer spans there was much less advantage. Sometimes southern pine was used for lower chord sticks in spans of 100' or more because it was difficult to find local spruce long enough.